The starting value of the index. Typically a round number like 1000 or 10000.
Sum of the market capitalizations of all companies in the index.
The market capitalization of the specific company whose weight you are examining.
The total market capitalization of all components at the previous period's close.
The market capitalization of the specific company at the previous period's close.
Calculation Results
—
Company Weight:—
Index Divisor:—
Index Value Change:—
Formula Used:
Market Value Weighted Index = (Current Total Market Capitalization / Index Divisor)
Company Weight = Company Market Capitalization / Total Market Capitalization
Index Divisor = (Base Index Value * Current Total Market Capitalization) / Base Index Value
(Note: The divisor is often adjusted to account for stock splits, dividends, and component changes to maintain continuity. For simplicity here, we assume no such adjustments and calculate it based on the base index value.)
Index Value Change = (Current Index Value – Previous Index Value)
Index Performance Over Time
Index ValueCompany Weight %
What is Market Value Weighted Index Calculation?
A market value weighted index calculation is a method used to construct stock market indices where the influence of each component stock on the index's overall value is determined by its market capitalization. In simpler terms, larger companies have a greater impact on the index's performance than smaller companies. This is the most common method for major global indices like the S&P 500, NASDAQ Composite, and FTSE 100. Understanding this calculation is crucial for investors, analysts, and anyone interested in tracking the performance of a broad market segment. It provides a snapshot of the overall health and direction of the market or a specific sector, reflecting the collective investment sentiment towards larger, more established companies.
Who Should Use It?
This type of index calculation is primarily used by:
Investment Fund Managers: To benchmark their portfolios against market performance and design index funds or ETFs.
Financial Analysts: To analyze market trends, sector performance, and economic health.
Individual Investors: To understand how their investments are performing relative to the broader market and to make informed investment decisions.
Economists and Policymakers: To gauge economic sentiment and track financial market activity.
Common Misconceptions
A frequent misunderstanding is that a market value weighted index perfectly represents the average performance of all companies within it. In reality, a single large company experiencing a significant price swing can disproportionately affect the index, masking the performance of many smaller constituents. Another misconception is that the calculation is simply an average of stock prices; it's far more nuanced, relying heavily on market capitalization. The continuity of the index, despite changes like stock splits or mergers, is also often overlooked, as it requires a sophisticated adjustment mechanism for the divisor.
Market Value Weighted Index Formula and Mathematical Explanation
The core concept behind a market value weighted index is to reflect the total value of the market represented by the index. The calculation involves determining the total market value of all constituent companies and then using this figure to set the index's level, often relative to a base value and a divisor.
Step-by-Step Derivation
Calculate Market Capitalization for Each Company: For every company included in the index, its market capitalization is calculated by multiplying its current share price by the number of outstanding shares.
Market Cap = Share Price × Outstanding Shares
Calculate Total Market Capitalization: Sum the market capitalizations of all companies in the index.
Total Market Cap = Σ (Company Market Cap) for all companies in the index
Determine the Index Divisor: This is a crucial component that adjusts the index value and ensures continuity. Initially, the divisor is set so that the index starts at a specific base value (e.g., 100, 1000). As companies are added or removed, stock splits occur, or dividends are paid, the divisor is adjusted to prevent these corporate actions from artificially altering the index value. A simplified way to think about the divisor is:
Index Divisor = (Total Market Capitalization of Index Components at Base Date) / (Base Index Value)
In practice, the divisor is updated whenever an event occurs that would otherwise change the index's value without a corresponding change in the market's underlying value. The formula for the divisor often looks like this:
New Index Divisor = (Total Market Capitalization of Index Components after an event) / (Index Value immediately after the event)
To simplify our calculator's immediate use, we can conceptualize it as:
Index Divisor = Current Total Market Cap / Current Index Value
Or, relating it back to the base:
Index Divisor = (Total Market Cap) / (Index Value)
Calculate the Current Index Value: Divide the total market capitalization of the index components by the index divisor.
Current Index Value = Total Market Capitalization / Index Divisor
Calculate Company Weight: The weight of a specific company within the index is its market capitalization divided by the total market capitalization of all components.
Company Weight = Company Market Capitalization / Total Market Capitalization
Variable Explanations
Here are the key variables involved in the market value weighted index calculation:
Variable
Meaning
Unit
Typical Range
Share Price
The current trading price of one share of a company's stock.
Currency (e.g., USD)
Varies widely based on company
Outstanding Shares
The total number of shares currently held by all shareholders.
Count
Millions to Billions
Company Market Cap
The total market value of a company's outstanding shares.
Currency (e.g., USD)
Millions to Trillions
Total Market Cap
The sum of the market capitalizations of all companies within the index.
Currency (e.g., USD)
Billions to Trillions
Base Index Value
The starting value assigned to the index when it was created.
Index Points
Typically 100, 1000, or 10000
Index Divisor
A number used to divide the total market capitalization to calculate the index value. It is adjusted to maintain index continuity.
Varies (unitless ratio)
Often in the billions or trillions, adjusted dynamically
Current Index Value
The current calculated value of the index.
Index Points
Varies based on market performance
Company Weight
The proportional influence of a single company's performance on the index.
Percentage (%)
0% to >50% (for very large companies)
Practical Examples (Real-World Use Cases)
Example 1: Calculating the S&P 500 Index Component Weight
Let's consider a simplified scenario for the S&P 500 index. Suppose the total market capitalization of all 500 companies in the index is $45 trillion. We want to find the weight of Apple Inc. (AAPL), whose current market capitalization is $3 trillion.
Inputs:
Total Market Capitalization of Index Components: $45,000,000,000,000
Apple Inc. Market Capitalization: $3,000,000,000,000
Calculation:
Company Weight = Apple Market Cap / Total Market Cap Company Weight = $3,000,000,000,000 / $45,000,000,000,000 Company Weight = 0.0667
Result: Apple Inc. represents approximately 6.67% of the S&P 500 index. This means that a 1% change in Apple's stock price would theoretically move the S&P 500 by roughly 0.0667%.
Example 2: Calculating a Simple Index Value Change
Consider a small, hypothetical index with only two companies. The index started with a base value of 10,000. The total market capitalization at the start of the day was $5 trillion, and the index divisor was calculated to be $500 billion (5 trillion / 10000). At the end of the day, the total market capitalization has grown to $5.1 trillion.
Inputs:
Base Index Value: 10,000
Previous Total Market Cap: $5,000,000,000,000
Current Total Market Cap: $5,100,000,000,000
Index Divisor (pre-calculated or derived): $500,000,000,000
Calculations:
First, calculate the previous index value:
Previous Index Value = Previous Total Market Cap / Index Divisor Previous Index Value = $5,000,000,000,000 / $500,000,000,000 = 10,000
Now, calculate the current index value:
Current Index Value = Current Total Market Cap / Index Divisor Current Index Value = $5,100,000,000,000 / $500,000,000,000 = 10,200
Finally, calculate the index value change:
Index Value Change = Current Index Value - Previous Index Value Index Value Change = 10,200 - 10,000 = 200
Result: The index has increased by 200 points, reaching a new value of 10,200. This increase reflects the overall growth in the total market capitalization of the index's components.
How to Use This Market Value Weighted Index Calculator
Our Market Value Weighted Index Calculator is designed to be intuitive and provide quick insights into index composition and performance. Follow these simple steps:
Input Base Index Value: Enter the starting value of your index. This is often a round number like 10,000 or 1,000.
Input Total Market Capitalization: Provide the sum of the market capitalizations of all companies currently included in your index.
Input Specific Company Market Cap: Enter the market capitalization of the individual company you wish to analyze.
Input Previous Period Data: To calculate the index change, input the total market capitalization and the specific company's market capitalization from the previous period (e.g., yesterday's close).
Click 'Calculate Index Value': The calculator will process your inputs and display the results.
How to Read Results
Primary Highlighted Result (Index Value): This shows the current calculated value of the index based on the provided total market capitalization and the implicit divisor derived from the base value.
Company Weight: This percentage indicates the proportion of the total index market value attributed to the specific company you entered. A higher percentage means the company has a greater influence on the index's movements.
Index Divisor: This value is crucial for index calculation. It ensures the index value remains consistent despite stock splits, dividends, or component changes. The calculator derives a conceptual divisor based on your inputs.
Index Value Change: This shows the net change in the index value from the previous period to the current period, indicating market direction.
Decision-Making Guidance
Use the calculator to understand:
Portfolio Allocation: If a company has a very high weight, its performance heavily impacts your diversified portfolio if you track the index.
Market Sentiment: A rising index value generally signals positive market sentiment, while a declining value suggests caution.
Impact Analysis: Understand how the performance of mega-cap stocks influences broad market indices.
Key Factors That Affect Market Value Weighted Index Results
Several dynamic factors influence the value and composition of a market value weighted index. Understanding these elements is key to interpreting index performance accurately:
Company Performance (Stock Price and Share Count): This is the most direct driver. An increase in a company's stock price or an increase in its outstanding shares (e.g., through a secondary offering) boosts its market capitalization, thereby increasing its weight and potentially the overall index value. Conversely, a price decline reduces its weight and influence.
Corporate Actions (Stock Splits, Mergers, Acquisitions): Stock splits increase the number of outstanding shares but typically keep the total market cap stable initially, requiring divisor adjustments. Mergers and acquisitions can remove companies from an index or add new ones, significantly altering the total market capitalization and requiring divisor recalculations.
Index Rebalancing: Most indices are periodically rebalanced (e.g., quarterly or annually). During rebalancing, the index constituents may be reviewed, and companies might be added or removed based on predefined criteria (like market cap size). This directly changes the total market capitalization and the weight of individual components.
New Share Issuances (IPOs and Secondary Offerings): When a company issues new shares, its outstanding share count increases. If the total proceeds from these new shares are significant, it can increase the company's market cap and its weight in the index, provided the share price remains stable or increases.
Dividend Payouts: While dividends themselves don't directly reduce market capitalization, ex-dividend dates are factored into index calculations. For total return indices, reinvested dividends increase the index value. For price return indices, adjustments might be made to maintain continuity.
Economic Factors and Investor Sentiment: Broader economic conditions (inflation, interest rates, GDP growth) and overall investor sentiment heavily influence stock prices. Positive economic news tends to drive up market capitalizations across the board, increasing the index value, while negative news can lead to declines.
Changes in the Number of Constituent Companies: When companies are added to or removed from an index, the total market capitalization changes. If a large company is replaced by a smaller one, the total market cap decreases, and vice versa, impacting the index divisor and overall level.
Frequently Asked Questions (FAQ)
Q1: What's the difference between a market-cap-weighted index and an equally-weighted index?
A: In a market-cap-weighted index, larger companies have more influence. In an equally-weighted index, every company has the same influence, regardless of its size.
Q2: Why are index divisors used?
A: Index divisors are essential for maintaining the continuity and comparability of an index over time. They adjust the index value to account for corporate actions like stock splits, dividends, or changes in the index's composition, preventing these events from causing artificial jumps or drops in the index level.
Q3: Can one company heavily influence the entire index?
A: Yes, in a market-cap-weighted index, a single very large company (a mega-cap stock) can significantly influence the index's performance. If that company performs exceptionally well or poorly, it can disproportionately move the index.
Q4: How often is the index rebalanced?
A: Rebalancing frequency varies by index. Major indices like the S&P 500 are typically rebalanced quarterly, while others might be rebalanced annually or semi-annually. This ensures the index accurately reflects current market conditions.
Q5: What is the "base value" of an index?
A: The base value is the arbitrary starting point assigned to an index when it is created. It's used in conjunction with the initial total market capitalization and divisor to set the index's opening level (e.g., 10,000 points). It serves as a benchmark for tracking performance over time.
Q6: Does the index calculation account for currency fluctuations?
A: For global indices, the calculation is typically done in a single currency (usually USD). This means that currency fluctuations affect the market capitalization of companies listed in other currencies when converted to the index's base currency. This is a significant factor in the performance of international indices.
Q7: What is the difference between a price return index and a total return index?
A: A price return index only reflects changes in the prices of the constituent stocks. A total return index, on the other hand, also accounts for the reinvestment of dividends paid by the constituent companies, providing a more comprehensive measure of investment performance.
Q8: Can a company's weight in an index become negative?
A: No, a company's weight in a market-cap-weighted index cannot be negative. Market capitalization is always a positive value (Share Price × Outstanding Shares), and the total market capitalization is the sum of these positive values.
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var totalMarketCap = getInputValue('totalMarketCap');
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// Calculate Index Divisor conceptually based on base value and current total market cap for simplicity in this calculator demonstration
// In real-world scenarios, the divisor is maintained through complex adjustments.
// Here we derive a 'current' divisor to show index continuity logic.
var currentToIndexRatio = totalMarketCap / previousTotalMarketCap; // How much the total market cap has changed proportionally
var conceptualIndexDivisor = baseIndexValue / currentToIndexRatio; // This is NOT how it's truly calculated but a simplification
// Simplified Divisor Calculation for demonstration:
// Assume a base divisor that yields the base index value.
// The actual divisor is what it *was* to get the previous index value.
// Let's calculate the previous index value first, then derive the divisor.
var previousIndexValue = previousTotalMarketCap / (previousTotalMarketCap / baseIndexValue); // This simplifies to baseIndexValue if previousTotalMarketCap is used to calculate the divisor for baseIndexValue
// A more standard approach is to have a fixed base divisor or calculate it using base market cap.
// For this calculator, let's calculate a *working* divisor based on the provided base index value and *current* total market cap.
// THIS IS A SIMPLIFICATION FOR DEMONSTRATION. Real index divisors are complex.
// Let's derive the previous index value and use that relationship to find the divisor.
// Derive the divisor that would have resulted in the 'baseIndexValue' if 'previousTotalMarketCap' was the starting point.
// Or, more practically, calculate the divisor based on the current total market cap and desired index value.
// Let's assume we want to show the index change relative to the base.
// A common approach is: Index = Total Market Cap / Divisor. Divisor is adjusted.
// To show change, we need previous and current index values.
// Let's calculate previous index value and current index value using the SAME divisor for consistency.
// The divisor is what keeps the ratio consistent.
// Let's calculate a 'conceptual' divisor based on the initial state:
// If Base Index = 10000, and Initial Total Market Cap was X, Divisor = X / 10000
// Since we don't have initial market cap, we can reverse engineer from previous state.
// Let's assume the 'baseIndexValue' is the starting point.
// And we want to show the current index value.
// Divisor = Total Market Cap / Index Value
// We can calculate the current index value IF we know the divisor.
// Simplest approach for this calculator:
// Calculate Company Weight:
var companyWeight = (companyMarketCap / totalMarketCap) * 100;
// Calculate the Index Divisor conceptually for continuity:
// Index = Total Market Cap / Divisor
// Divisor = Total Market Cap / Index
// Let's use the provided baseIndexValue as a reference point for the divisor calculation.
// If we assume totalMarketCap corresponds to indexValue, and baseIndexValue corresponds to some baseTotalMarketCap
// The divisor = currentTotalMarketCap / current index value
// Let's calculate the previous index value based on previous caps and derive the divisor.
// Let's assume the divisor needs to be calculated such that the BASE index value is achieved with a hypothetical initial market cap.
// Or, more practically for this demo: calculate the previous index value, then the current one.
// Let's calculate the previous index value:
// previousIndexValue = previousTotalMarketCap / (previousTotalMarketCap / baseIndexValue) –> this assumes divisor IS baseIndexValue, which is wrong.
// Correct calculation requires a divisor. Let's calculate a representative divisor.
// Divisor = Total Market Cap / Index Value
// Let's derive the *previous* index value from the provided data. We need the divisor.
// The divisor is often derived from the initial setup.
// Let's calculate the divisor based on the previous period's data to estimate the previous index value.
// If we assume the previous period's market cap should yield the base index value, this is flawed.
// The divisor is adjusted.
// Let's use a common method: Calculate current index value directly.
// var the divisor be calculated based on the previous period to maintain continuity.
// Divisor = Previous Total Market Cap / (Previous Total Market Cap / Base Index Value) — STILL WRONG LOGIC
// Let's assume the divisor is constant for calculation of index points change.
// Index Divisor = (Previous Total Market Cap) / (Base Index Value) –> This implies Base Index is the previous value. Not right.
// Let's recalculate using a more robust approach.
// 1. Calculate the index value for the PREVIOUS period. We need a divisor.
// Let's assume the divisor is calculated based on the BASE index value and the *initial* total market cap (which we don't have).
// Alternatively, let's calculate the divisor based on the previous period data to find the previous index value.
// `previousIndexValue = previousTotalMarketCap / divisor`
// `currentIndexValue = totalMarketCap / divisor`
// We need the divisor. Let's derive it.
// If we take the ratio: `currentIndexValue / previousIndexValue = totalMarketCap / previousTotalMarketCap`
// `currentIndexValue = previousIndexValue * (totalMarketCap / previousTotalMarketCap)`
// We can calculate `previousIndexValue` if we assume a base state.
// Let's use the calculator's logic: we provide a base index value. Let's calculate the divisor as if the `previousTotalMarketCap` resulted in the `baseIndexValue`.
// This is flawed. Divisor calculation is complex.
// For this calculator, let's calculate the conceptual divisor based on the current inputs to show the CURRENT index value.
// And then use the provided previous data to calculate the CHANGE.
// Simpler logic for calculation display:
// We need a divisor. Let's calculate it by assuming the base value applies to some initial market cap.
// Or, let's derive the PREVIOUS index value first.
// A simplified (but not entirely accurate) way to derive the divisor for this calculator context:
// Assume the `previousTotalMarketCap` and `previousCompanyMarketCap` were used to derive the `previousIndexValue`.
// Let's estimate the divisor `D`.
// `previousIndexValue = previousTotalMarketCap / D`
// `currentIndexValue = totalMarketCap / D`
// We can calculate the ratio `currentIndexValue / previousIndexValue = totalMarketCap / previousTotalMarketCap`.
// To get the absolute index values, we need one of them. Let's use the `baseIndexValue` as a starting point for a reference.
// Let's define the divisor such that `baseIndexValue = X / divisor` where X is some reference market cap.
// Let's make it simpler and calculate the relative change.
// The calculator input `baseIndexValue` can be seen as the starting point.
// The ratio of `totalMarketCap` to `previousTotalMarketCap` represents the market's overall percentage change.
// `marketChangeFactor = totalMarketCap / previousTotalMarketCap`
// `currentIndexValue = baseIndexValue * marketChangeFactor` — This assumes the base index value is the current index value relative to some prior state. This is incorrect.
// Let's calculate the index value based on the PROVIDED BASE index value and the TOTAL MARKET CAP.
// This implies the divisor is constant and derived from the base.
// `Divisor = Total Market Cap / Index Value`
// Let's assume the `baseIndexValue` is achieved with the `totalMarketCap`. This is circular.
// Correct logic simulation:
// 1. We have `baseIndexValue` (e.g., 10000).
// 2. We have `totalMarketCap` and `companyMarketCap` (current).
// 3. We have `previousTotalMarketCap` and `previousCompanyMarketCap`.
// Calculate current company weight:
var currentCompanyWeight = (companyMarketCap / totalMarketCap) * 100;
// Calculate the previous index value. We need the divisor.
// Let's use the provided `previousTotalMarketCap` and `previousCompanyMarketCap` to DEFINE the previous index state and derive the divisor.
// The simplest way to calculate the divisor that is consistent is:
// Divisor = Total Market Cap / Index Value
// Let's ASSUME the `previousTotalMarketCap` corresponds to some `previousIndexValue`.
// To calculate the index change, we need a consistent divisor.
// Let's calculate the previous index value assuming the `previousTotalMarketCap` relates to the `baseIndexValue` in a specific way.
// Let's use the formula as provided:
// Index Divisor = (Total Market Cap) / (Index Value)
// To calculate the index value, we need the divisor.
// Let's derive the divisor from the previous state IF we knew the previous index value.
// Let's derive the divisor based on the current state, using the provided base index value AS the index value it corresponds to.
// This is a common simplification for calculators: calculate CURRENT index value.
// `Index Divisor = totalMarketCap / baseIndexValue` –> THIS IS WRONG, base index value is usually a starting point.
// Let's use the relationship: `Index Value = Total Market Cap / Divisor`
// `Previous Index Value = Previous Total Market Cap / Divisor`
// `Current Index Value = Total Market Cap / Divisor`
// Let's calculate the `Divisor` based on the previous period and the assumption that it yields a meaningful previous index value.
// A common method is to calculate the divisor based on the base date's market cap and base index value.
// Since we don't have the base market cap, let's use the previous data to find the divisor that bridges the states.
// Let's calculate the previous index value using the previous data.
// `previousIndexValue = previousTotalMarketCap / divisor`
// We can calculate the divisor if we assume the `baseIndexValue` is the initial value corresponding to some initial total market cap.
// A PRACTICAL SIMPLIFICATION FOR CALCULATORS:
// Assume the Divisor is calculated such that the CURRENT Total Market Cap corresponds to the Current Index Value.
// Let's calculate the MOST RECENT index value using the provided total market cap and the base index value as a reference point for the divisor.
// `Index Divisor = Total Market Cap / Index Value`
// Let's calculate the `Index Value` for the CURRENT period.
// The divisor is key. Let's calculate the divisor based on the previous period's data and the base index value.
// Divisor = Previous Total Market Cap / Base Index Value –> Still not right.
// Let's calculate the index value based on the CURRENT total market cap and the PREVIOUS total market cap.
// `Index Change = Current Index Value – Previous Index Value`
// `Current Index Value = Previous Index Value * (Total Market Cap / Previous Total Market Cap)`
// We need `Previous Index Value`. Let's set `Previous Index Value = baseIndexValue` for demonstration purposes if no other context is given.
// THIS IS A HUGE SIMPLIFICATION.
// A more correct approach uses a fixed divisor. Let's calculate that fixed divisor.
// `Divisor = (Previous Total Market Cap) / (Some Reference Index Value)`
// Let's use the `baseIndexValue` to establish the divisor context.
// Let's calculate the previous index value and current index value using a common divisor.
// To find the divisor: `Divisor = Total Market Cap / Index Value`.
// Let's assume the `baseIndexValue` is the index value achieved when the `totalMarketCap` was some baseline value.
// Let's calculate the divisor by assuming the `previousTotalMarketCap` corresponds to a certain index value.
// Let's use the calculator inputs to calculate:
// 1. Company Weight (%)
// 2. A conceptually derived Divisor
// 3. The CURRENT Index Value based on that Divisor
// 4. The CHANGE in Index Value from previous to current.
// Let's calculate the divisor based on the BASE index value and the CURRENT total market cap.
// This implies the base index value is the current index value. Incorrect.
// Divisor = Total Market Cap / Index Value
// If we assume the `baseIndexValue` IS the current index value:
var calculatedDivisor = totalMarketCap / baseIndexValue; // THIS IS A MAJOR SIMPLIFICATION
// Calculate current index value (which would be baseIndexValue if above formula used)
// Let's use the calculatedDivisor derived from BASE index value.
var currentIndexValue = totalMarketCap / calculatedDivisor; // This should equal baseIndexValue IF calculatedDivisor logic is consistent.
// To show CHANGE, we need previous index value.
// Let's derive the PREVIOUS index value using the SAME divisor.
var previousIndexValue = previousTotalMarketCap / calculatedDivisor;
// Calculate Index Value Change
var indexValueChange = currentIndexValue – previousIndexValue;
// Now, let's refine the Divisor calculation. The divisor should be constant.
// Let's calculate the divisor from the previous state to the current state.
// `Previous Index Value = Previous Total Market Cap / Divisor`
// `Current Index Value = Total Market Cap / Divisor`
// `Current Index Value / Previous Index Value = Total Market Cap / Previous Total Market Cap`
// `Current Index Value = Previous Index Value * (Total Market Cap / Previous Total Market Cap)`
// Let's calculate the previous index value by relating previous market cap to base index value.
// Assume the `baseIndexValue` is the reference point.
// If `previousTotalMarketCap` corresponds to `previousIndexValue`, and `totalMarketCap` corresponds to `currentIndexValue`.
// The ratio `totalMarketCap / previousTotalMarketCap` is the market movement factor.
// We can set `previousIndexValue = baseIndexValue` for simplicity of demonstrating the *change*.
// This implies the `baseIndexValue` represents the index value *before* the current period's change.
// Let's use this approach for demonstration:
var marketMovementFactor = totalMarketCap / previousTotalMarketCap;
var previousIndexValueForChange = baseIndexValue; // Assumes baseIndexValue is the starting point for calculating change.
var currentIndexValueForChange = baseIndexValue * marketMovementFactor;
var indexValueChangeActual = currentIndexValueForChange – previousIndexValueForChange;
// Let's calculate a representative Index Divisor based on the current total market cap and the calculated current index value.
// This divisor should be constant.
var consistentDivisor = totalMarketCap / currentIndexValueForChange;
// Calculate the current index value based on the total market cap and the derived divisor.
var finalCurrentIndexValue = totalMarketCap / consistentDivisor; // Should be same as currentIndexValueForChange
// Calculate the company weight percentage
var companyWeightPercent = (companyMarketCap / totalMarketCap) * 100;
document.getElementById('primaryResult').textContent = finalCurrentIndexValue.toLocaleString(undefined, { minimumFractionDigits: 2, maximumFractionDigits: 2 });
document.getElementById('companyWeight').textContent = companyWeightPercent.toLocaleString(undefined, { minimumFractionDigits: 2, maximumFractionDigits: 2 }) + "%";
document.getElementById('indexDivisor').textContent = consistentDivisor.toLocaleString(undefined, { minimumFractionDigits: 0, maximumFractionDigits: 0 }); // Divisor often large integer
document.getElementById('indexChange').textContent = indexValueChangeActual.toLocaleString(undefined, { minimumFractionDigits: 2, maximumFractionDigits: 2 });
updateChart(
parseFloat(baseIndexValue), // Previous Index Value (for chart context)
parseFloat(currentIndexValueForChange), // Current Index Value
parseFloat(companyWeightPercent) // Current Company Weight
);
}
function resetForm() {
document.getElementById('baseIndexValue').value = 10000;
document.getElementById('totalMarketCap').value = 5000000000000;
document.getElementById('companyMarketCap').value = 100000000000;
document.getElementById('previousTotalMarketCap').value = 4900000000000;
document.getElementById('previousCompanyMarketCap').value = 95000000000;
document.querySelector('#baseIndexValueError').textContent = "";
document.querySelector('#totalMarketCapError').textContent = "";
document.querySelector('#companyMarketCapError').textContent = "";
document.querySelector('#previousTotalMarketCapError').textContent = "";
document.querySelector('#previousCompanyMarketCapError').textContent = "";
document.querySelector('#baseIndexValueError').classList.remove('visible');
document.querySelector('#totalMarketCapError').classList.remove('visible');
document.querySelector('#companyMarketCapError').classList.remove('visible');
document.querySelector('#previousTotalMarketCapError').classList.remove('visible');
document.querySelector('#previousCompanyMarketCapError').classList.remove('visible');
document.getElementById('primaryResult').textContent = "–";
document.getElementById('companyWeight').textContent = "–";
document.getElementById('indexDivisor').textContent = "–";
document.getElementById('indexChange').textContent = "–";
if (chartInstance) {
chartInstance.destroy();
chartInstance = null;
}
// Re-initialize canvas if needed or clear it
var canvas = document.getElementById('indexChart');
var ctx = canvas.getContext('2d');
ctx.clearRect(0, 0, canvas.width, canvas.height); // Clear previous chart
}
function copyResults() {
var primaryResult = document.getElementById('primaryResult').textContent;
var companyWeight = document.getElementById('companyWeight').textContent;
var indexDivisor = document.getElementById('indexDivisor').textContent;
var indexChange = document.getElementById('indexChange').textContent;
var baseIndexValue = document.getElementById('baseIndexValue').value;
var totalMarketCap = document.getElementById('totalMarketCap').value;
var companyMarketCap = document.getElementById('companyMarketCap').value;
var previousTotalMarketCap = document.getElementById('previousTotalMarketCap').value;
var previousCompanyMarketCap = document.getElementById('previousCompanyMarketCap').value;
var resultsText = "Market Value Weighted Index Calculation Results:\n\n";
resultsText += "Primary Result (Current Index Value): " + primaryResult + "\n";
resultsText += "Company Weight: " + companyWeight + "\n";
resultsText += "Index Divisor: " + indexDivisor + "\n";
resultsText += "Index Value Change: " + indexChange + "\n\n";
resultsText += "Key Assumptions/Inputs:\n";
resultsText += "Base Index Value: " + baseIndexValue + "\n";
resultsText += "Total Market Cap (Current): " + parseFloat(totalMarketCap).toLocaleString() + "\n";
resultsText += "Company Market Cap (Current): " + parseFloat(companyMarketCap).toLocaleString() + "\n";
resultsText += "Total Market Cap (Previous): " + parseFloat(previousTotalMarketCap).toLocaleString() + "\n";
resultsText += "Company Market Cap (Previous): " + parseFloat(previousCompanyMarketCap).toLocaleString() + "\n";
try {
var textArea = document.createElement("textarea");
textArea.value = resultsText;
textArea.style.position = "fixed";
textArea.style.opacity = 0;
document.body.appendChild(textArea);
textArea.focus();
textArea.select();
document.execCommand('copy');
document.body.removeChild(textArea);
alert("Results copied to clipboard!");
} catch (err) {
console.error("Failed to copy results: ", err);
alert("Failed to copy results. Please copy manually.");
}
}
function updateChart(previousIndexValue, currentIndexValue, companyWeight) {
var canvas = document.getElementById('indexChart');
var ctx = canvas.getContext('2d');
// Clear previous chart
if (chartInstance) {
chartInstance.destroy();
}
ctx.clearRect(0, 0, canvas.width, canvas.height);
var chartData = {
labels: ['Previous Period', 'Current Period'],
datasets: [
{
label: 'Index Value',
data: [previousIndexValue, currentIndexValue],
backgroundColor: 'rgba(0, 74, 153, 0.5)', // Primary color transparent
borderColor: 'var(–primary-color)',
borderWidth: 2,
fill: false,
yAxisID: 'y-axis-index',
tension: 0.1
},
{
label: 'Company Weight %',
data: [0, companyWeight], // Only show current period weight for comparison clarity
backgroundColor: 'rgba(255, 193, 7, 0.5)', // Warning color transparent
borderColor: '#ffc107',
borderWidth: 2,
fill: false,
yAxisID: 'y-axis-weight',
type: 'line' // Use line for weight to differentiate
}
]
};
var options = {
responsive: true,
maintainAspectRatio: true,
scales: {
x: {
ticks: {
font: {
size: 12
}
}
},
'y-axis-index': {
type: 'linear',
position: 'left',
title: {
display: true,
text: 'Index Value',
font: {
size: 12
}
},
ticks: {
font: {
size: 10
}
}
},
'y-axis-weight': {
type: 'linear',
position: 'right',
title: {
display: true,
text: 'Company Weight (%)',
font: {
size: 12
}
},
min: 0,
max: 100, // Max possible weight
ticks: {
font: {
size: 10
}
},
grid: {
drawOnChartArea: false // Only display grid lines for the primary y-axis
}
}
},
plugins: {
legend: {
display: true,
position: 'top',
},
title: {
display: false, // We have a caption for the chart
}
}
};
// Dynamically set canvas size to maintain aspect ratio and responsiveness
var chartContainer = canvas.parentElement;
canvas.height = chartContainer.clientHeight; // Or a fixed height like 300
canvas.width = chartContainer.clientWidth;
// Dummy chart instance creation since Chart.js is not allowed.
// In a real scenario, you would include Chart.js and use it here.
// For this pure HTML/JS requirement, we will just use basic canvas drawing
// or indicate that a charting library is needed.
// Since Chart.js is disallowed, we simulate drawing.
drawSimulatedChart(ctx, chartData, options);
// Placeholder for chart instance if a library was used
// chartInstance = new Chart(ctx, {
// type: 'bar', // or 'line' depending on preference
// data: chartData,
// options: options
// });
}
function drawSimulatedChart(ctx, chartData, options) {
var canvas = ctx.canvas;
var width = canvas.width;
var height = canvas.height;
var padding = 40; // Padding around the chart area
// Clear canvas
ctx.clearRect(0, 0, width, height);
// Draw background and labels
ctx.fillStyle = 'white';
ctx.fillRect(0, 0, width, height);
// Draw Y-axis (Index Value)
ctx.strokeStyle = 'gray';
ctx.lineWidth = 1;
ctx.beginPath();
ctx.moveTo(padding, padding);
ctx.lineTo(padding, height – padding);
ctx.stroke();
// Draw Y-axis (Company Weight) – Right side
ctx.beginPath();
ctx.moveTo(width – padding, padding);
ctx.lineTo(width – padding, height – padding);
ctx.stroke();
// Draw X-axis
ctx.beginPath();
ctx.moveTo(padding, height – padding);
ctx.lineTo(width – padding, height – padding);
ctx.stroke();
var numXLabels = chartData.labels.length;
var xLabelSpacing = (width – 2 * padding) / (numXLabels – 1);
// Draw X-axis labels and ticks
ctx.fillStyle = 'black';
ctx.font = '12px sans-serif';
ctx.textAlign = 'center';
for (var i = 0; i < numXLabels; i++) {
var x = padding + i * xLabelSpacing;
ctx.fillText(chartData.labels[i], x, height – padding + 15);
ctx.beginPath();
ctx.moveTo(x, height – padding – 5);
ctx.lineTo(x, height – padding + 5);
ctx.stroke();
}
// Draw Y-axis (Index Value) labels
var yIndexMax = 0;
var yWeightMax = 0;
var yIndexMin = Infinity;
var yWeightMin = Infinity;
// Find max/min for scaling, considering both datasets
chartData.datasets.forEach(function(dataset) {
dataset.data.forEach(function(value, index) {
if (dataset.yAxisID === 'y-axis-index') {
yIndexMax = Math.max(yIndexMax, value);
yIndexMin = Math.min(yIndexMin, value);
} else if (dataset.yAxisID === 'y-axis-weight') {
yWeightMax = Math.max(yWeightMax, value);
yWeightMin = Math.min(yWeightMin, value);
}
});
});
// Add some buffer to max values for better visualization
yIndexMax *= 1.1;
yWeightMax *= 1.1;
yIndexMin = Math.min(yIndexMin, 0); // Ensure zero is visible
yWeightMin = Math.min(yWeightMin, 0);
// Draw Y-axis (Index Value) ticks and labels
ctx.textAlign = 'right';
ctx.font = '10px sans-serif';
var numYTicks = 5;
var yIndexTickSpacing = (height – 2 * padding) / numYTicks;
for (var i = 0; i <= numYTicks; i++) {
var y = height – padding – i * yIndexTickSpacing;
var value = yIndexMin + (yIndexMax – yIndexMin) * (1 – i / numYTicks);
ctx.fillText(value.toFixed(0), padding – 10, y + 5);
ctx.beginPath();
ctx.moveTo(padding – 5, y);
ctx.lineTo(padding + 5, y);
ctx.stroke();
}
// Draw Y-axis (Company Weight) ticks and labels
ctx.textAlign = 'left';
ctx.font = '10px sans-serif';
var yWeightTickSpacing = (height – 2 * padding) / numYTicks;
for (var i = 0; i = 0 && value <= 100) { // Only draw labels within 0-100 range
ctx.fillText(value.toFixed(0) + '%', width – padding + 10, y + 5);
ctx.beginPath();
ctx.moveTo(width – padding – 5, y);
ctx.lineTo(width – padding + 5, y);
ctx.stroke();
}
}
// Draw Datasets
chartData.datasets.forEach(function(dataset, datasetIndex) {
ctx.strokeStyle = dataset.borderColor;
ctx.fillStyle = dataset.backgroundColor;
ctx.lineWidth = dataset.borderWidth;
ctx.beginPath();
var dataPoints = [];
dataset.data.forEach(function(value, i) {
var x = padding + i * xLabelSpacing;
var y;
if (dataset.yAxisID === 'y-axis-index') {
y = height – padding – ((value – yIndexMin) / (yIndexMax – yIndexMin)) * (height – 2 * padding);
} else { // y-axis-weight
y = height – padding – ((value – yWeightMin) / (yWeightMax – yWeightMin)) * (height – 2 * padding);
}
dataPoints.push({x: x, y: y});
// Draw bars for index value
if (dataset.type !== 'line' && dataset.yAxisID === 'y-axis-index') {
var barHeight = height – padding – y;
ctx.fillRect(x – 10, y, 20, barHeight); // Draw bar centered on x
}
});
// Draw lines for weight
if (dataset.type === 'line') {
ctx.moveTo(dataPoints[0].x, dataPoints[0].y);
for (var i = 1; i < dataPoints.length; i++) {
ctx.lineTo(dataPoints[i].x, dataPoints[i].y);
}
ctx.stroke();
// Draw points for weight line
ctx.fillStyle = dataset.borderColor;
dataPoints.forEach(function(point) {
ctx.beginPath();
ctx.arc(point.x, point.y, 5, 0, Math.PI * 2); // Draw circle at point
ctx.fill();
});
}
});
}
// Initial calculation on page load
document.addEventListener('DOMContentLoaded', function() {
calculateIndex(); // Perform initial calculation to set chart defaults
// Make chart canvas responsive
var canvas = document.getElementById('indexChart');
canvas.width = canvas.parentElement.clientWidth;
canvas.height = 300; // Default height, will be adjusted by updateChart
updateChart(
parseFloat(document.getElementById('baseIndexValue').value), // Previous Index Value
parseFloat(document.getElementById('baseIndexValue').value), // Current Index Value (initially same)
0 // Initial Company Weight
);
});