Estimate your monthly mortgage payments with our easy-to-use home loan calculator.
Mortgage Calculator
Enter the details of your potential home loan to estimate your monthly payments.
The total amount you wish to borrow.
The yearly interest rate offered by the lender.
The total duration of the loan in years.
The date your loan begins. Used for amortization schedule.
Your Estimated Mortgage Payment
$0.00
This is your estimated principal and interest payment per month.
Total Interest Paid: $0.00
Total Repayment: $0.00
Loan End Date: N/A
Key Assumptions:
Loan Amount: $0
Annual Interest Rate: 0%
Loan Term: 0 Years
Loan Amortization Chart
Visual representation of how your principal and interest payments change over time.
Amortization Schedule
Payment #
Date
Starting Balance
Payment
Principal
Interest
Ending Balance
A detailed breakdown of each payment towards principal and interest over the life of the loan.
What is a Home Loan Calculator?
A home loan calculator, also commonly referred to as a mortgage calculator, is an online tool designed to help prospective homebuyers and existing homeowners estimate the potential monthly payments for a home loan. It takes key financial inputs such as the loan amount, annual interest rate, and loan term, and uses them to project the principal and interest payments you would be required to make each month. This indispensable tool is a cornerstone for financial planning when purchasing property, allowing individuals to understand their borrowing capacity and the long-term financial commitment involved. It helps demystify the complex mathematics behind mortgages, making the home buying process more transparent and manageable. The core function of a free calculator for home loan is to provide a clear, quantifiable estimate of affordability. It serves as a crucial first step for anyone considering taking out a mortgage, enabling them to compare different loan scenarios and lender offers effectively. Understanding these estimates early on can prevent financial strain later by ensuring you only borrow what you can comfortably repay.
Who should use a home loan calculator? Anyone planning to buy a home, refinance an existing mortgage, or simply understand the cost of homeownership should use this tool. This includes first-time homebuyers, seasoned investors, individuals looking to leverage home equity, and those comparing loan offers. It's particularly valuable for understanding how different interest rates or loan terms impact your monthly budget. Even if you're just exploring possibilities, a home loan calculator provides vital insights into the financial landscape of homeownership.
Common misconceptions about home loan calculations: A frequent misunderstanding is that the calculator provides a guaranteed loan offer. It is merely an estimate based on the inputs provided. Lenders will perform their own detailed credit assessments and may offer different rates or terms. Another misconception is that the calculated payment includes all homeownership costs. Property taxes, homeowner's insurance, and potentially private mortgage insurance (PMI) or homeowner association (HOA) fees are often added to the P&I payment to form the total monthly housing expense (often called PITI – Principal, Interest, Taxes, and Insurance), which this basic calculator doesn't include by default. It's essential to remember that this free calculator for home loan provides a foundational estimate.
Home Loan Calculator Formula and Mathematical Explanation
The primary calculation performed by a home loan calculator is determining the fixed monthly payment (M) for a loan using the standard annuity formula. This formula ensures that over the loan's term, the loan is fully amortized – meaning it's paid off entirely through a series of equal payments, with each payment covering both interest and a portion of the principal.
The Mortgage Payment Formula (Amortization Formula)
The formula used is:
M = P [ i(1 + i)^n ] / [ (1 + i)^n – 1]
Variable Explanations:
M = Your total monthly mortgage payment (Principal & Interest)
P = The principal loan amount (the total amount you borrow)
i = Your monthly interest rate. This is calculated by dividing your annual interest rate by 12. (e.g., 5% annual rate = 0.05 / 12 = 0.004167 monthly rate)
n = The total number of payments over the loan's lifetime. This is calculated by multiplying the number of years in your loan term by 12. (e.g., a 30-year loan has 30 * 12 = 360 payments)
Variables Table:
Variable
Meaning
Unit
Typical Range
P (Loan Amount)
The total amount borrowed for the home purchase.
Currency ($)
$50,000 – $5,000,000+
Annual Interest Rate
The yearly percentage charged by the lender.
Percentage (%)
1% – 15%+ (Varies significantly with market conditions and borrower creditworthiness)
Loan Term
The duration over which the loan must be repaid.
Years
10, 15, 20, 30 years are common
i (Monthly Interest Rate)
The interest rate applied each month. Calculated as Annual Rate / 12.
Decimal (e.g., 0.004167 for 5% annual rate)
Calculated value based on annual rate
n (Number of Payments)
Total number of monthly payments. Calculated as Loan Term (Years) * 12.
Count
Calculated value based on loan term
M (Monthly Payment)
The fixed amount paid each month covering principal and interest.
Currency ($)
Calculated value
Calculation Breakdown:
Calculate Monthly Interest Rate (i): Divide the annual interest rate (as a decimal) by 12.
Calculate Total Number of Payments (n): Multiply the loan term in years by 12.
Calculate the Annuity Factor: This involves the terms `(1 + i)^n`.
Apply the Formula: Plug P, i, and n into the main formula to find M.
The calculator also computes Total Interest Paid (M * n – P) and Total Repayment (M * n). The amortization schedule breaks down each payment's allocation to principal and interest over time. This free calculator for home loan uses these standard financial formulas.
Practical Examples (Real-World Use Cases)
Example 1: First-Time Homebuyer
Sarah is looking to buy her first home. She's pre-approved for a loan of $300,000 at an annual interest rate of 6.5% for a term of 30 years. She wants to know her estimated monthly mortgage payment.
Inputs:
Loan Amount (P): $300,000
Annual Interest Rate: 6.5%
Loan Term: 30 years
Calculated Results:
Monthly Payment (M): Approximately $1,896.20
Total Interest Paid: Approximately $382,631.54
Total Repayment: Approximately $682,631.54
Financial Interpretation: Sarah's estimated monthly principal and interest payment is $1,896.20. Over 30 years, she will pay nearly as much in interest as her original loan amount. This highlights the significant long-term cost of borrowing. She might consider increasing her down payment or loan term if this payment is too high for her budget, or look for properties within a lower price range.
Example 2: Refinancing a Mortgage
John and Jane have an existing mortgage of $200,000 remaining on a 15-year loan term, with 10 years left. They currently pay 7.5% interest. They find a lender offering a refinance option at 6.0% interest for a new 15-year term, keeping their monthly payments similar but paying off the loan faster and saving on interest.
Inputs (New Loan):
Loan Amount (P): $200,000
Annual Interest Rate: 6.0%
Loan Term: 15 years
Calculated Results (New Loan):
Monthly Payment (M): Approximately $1,687.71
Total Interest Paid: Approximately $103,787.97
Total Repayment: Approximately $303,787.97
Financial Interpretation: Their current payment on the old loan (calculated separately) might be higher than $1,687.71. By refinancing, they secure a lower interest rate, resulting in a new estimated monthly payment of $1,687.71. This allows them to pay off their mortgage faster (15 years vs. remaining 10 years on old loan, but with a lower rate) and save substantially on total interest paid over the life of the loan. This is a strategic move to reduce their overall borrowing cost.
How to Use This Free Home Loan Calculator
Using our free calculator for home loan is straightforward. Follow these steps to get your mortgage payment estimates:
Enter Loan Amount: Input the total amount you plan to borrow for your home purchase. This is the principal (P) of your loan.
Enter Annual Interest Rate: Provide the yearly interest rate offered by the lender. This is crucial for calculating your monthly interest. Remember, even small differences in rates significantly impact your total payments.
Enter Loan Term: Specify the number of years you intend to take to repay the loan (e.g., 15, 20, or 30 years). A longer term means lower monthly payments but more total interest paid over time.
Select Loan Start Date: Choose the date your mortgage begins. This helps in generating an accurate amortization schedule.
Click 'Calculate': Once all fields are filled, click the 'Calculate' button. The calculator will instantly display your estimated monthly principal and interest payment.
How to Read Results:
Primary Result (Monthly Payment): This is your estimated fixed payment for principal and interest each month. Note that this typically excludes property taxes, homeowner's insurance, and other potential fees (PITI).
Total Interest Paid: This shows the total amount of interest you will pay over the entire life of the loan based on your inputs.
Total Repayment: This is the sum of the loan principal and all the interest paid over the loan term.
Loan End Date: The projected date your loan will be fully paid off.
Amortization Schedule & Chart: These provide a detailed breakdown of how each payment is allocated to principal and interest, and how your loan balance decreases over time.
Decision-Making Guidance:
Use the results to:
– Assess Affordability: Does the estimated monthly payment fit comfortably within your budget? Consider adding estimates for taxes and insurance to get a full picture.
– Compare Loan Options: Input different loan amounts, interest rates, or terms to see how they affect your payments. This helps you negotiate better terms or choose the loan that best suits your financial goals.
– Plan Savings: Understand the total interest paid to gauge the long-term cost of the loan and explore options to pay it down faster (e.g., extra payments).
Key Factors That Affect Home Loan Results
Several critical factors influence the outcome of your home loan calculator results and the actual mortgage you secure:
Interest Rate: This is arguably the most significant factor. A higher interest rate dramatically increases your monthly payment and the total interest paid over the loan's life. It's influenced by market conditions (like the Federal Reserve's policy rates), your credit score, loan type, and loan term.
Loan Term: A longer loan term (e.g., 30 years vs. 15 years) results in lower monthly payments but significantly higher total interest paid over time. Conversely, a shorter term means higher monthly payments but less overall interest.
Loan Amount (Principal): The larger the amount you borrow, the higher your monthly payments and total interest will be, assuming other factors remain constant. Increasing your down payment reduces the loan principal needed.
Credit Score: A higher credit score typically qualifies you for lower interest rates, directly reducing your monthly payments and total interest cost. Lenders see borrowers with good credit as lower risk.
Down Payment: A larger down payment reduces the principal loan amount required. This not only lowers your monthly payments but can also help you avoid Private Mortgage Insurance (PMI) if you reach the 20% equity threshold.
Fees and Closing Costs: While not always included in basic calculators, origination fees, appraisal fees, title insurance, and other closing costs add to the overall expense of obtaining a mortgage. These can sometimes be rolled into the loan amount, increasing the principal and thus the payments.
Loan Type (Fixed vs. Adjustable): This calculator assumes a fixed-rate mortgage. Adjustable-Rate Mortgages (ARMs) start with a lower introductory rate that can change over time, making future payments uncertain. Our calculator provides a fixed estimate.
Frequently Asked Questions (FAQ)
What is the difference between Principal and Interest?
The principal is the original amount of money borrowed. Interest is the fee charged by the lender for lending you money. Each mortgage payment consists of a portion that goes towards the principal and a portion that goes towards the interest.
Does the calculator include property taxes and insurance?
No, this basic home loan calculator typically estimates only the principal and interest (P&I) portion of your mortgage payment. Property taxes, homeowner's insurance, and potentially PMI or HOA fees are usually paid in addition to this amount, forming what's known as PITI (Principal, Interest, Taxes, and Insurance).
Can I use this calculator to estimate my refinance payment?
Yes, absolutely. Simply enter the remaining balance of your current mortgage as the 'Loan Amount', the new interest rate you've been offered as the 'Annual Interest Rate', and the remaining or desired term as the 'Loan Term'.
What does 'Amortization' mean?
Amortization is the process of paying off a debt (like a mortgage) over time through regular payments. With each payment, a portion goes to interest and a portion goes to principal. Early in the loan term, more of your payment goes towards interest; later, more goes towards principal.
How does my credit score affect my home loan calculation?
Your credit score significantly impacts the interest rate you'll be offered. A higher score generally means a lower interest rate, which reduces your monthly payments and the total interest paid, making your loan more affordable overall.
What is PMI and do I need to include it?
Private Mortgage Insurance (PMI) is typically required if your down payment is less than 20% of the home's purchase price. It protects the lender, not you. While this calculator doesn't automatically include PMI, you should factor its potential cost (usually 0.5% to 1% of the loan amount annually, divided by 12) into your total monthly housing budget.
What is the best loan term for me?
The "best" loan term depends on your financial situation and goals. A 15-year term usually has a lower interest rate and less total interest paid but higher monthly payments. A 30-year term has lower monthly payments but more total interest. Consider your budget and how long you plan to stay in the home.
Are there other costs associated with getting a home loan besides the payment?
Yes, besides the P&I payment, you'll encounter closing costs (appraisal fees, origination fees, title insurance, etc.), potential PMI, property taxes, and homeowner's insurance. Always budget for these additional expenses.
var chartInstance = null; // Global variable for chart instance
function validateInput(value, id, min, max, name) {
var errorElement = document.getElementById(id + 'Error');
errorElement.style.display = 'none';
if (value === "") {
errorElement.textContent = name + " cannot be empty.";
errorElement.style.display = 'block';
return false;
}
var numValue = parseFloat(value);
if (isNaN(numValue)) {
errorElement.textContent = name + " must be a valid number.";
errorElement.style.display = 'block';
return false;
}
if (min !== undefined && numValue max) {
errorElement.textContent = name + " cannot be greater than " + max + ".";
errorElement.style.display = 'block';
return false;
}
return true;
}
function calculateMortgage() {
var loanAmountInput = document.getElementById("loanAmount");
var annualInterestRateInput = document.getElementById("annualInterestRate");
var loanTermInput = document.getElementById("loanTerm");
var loanStartDateInput = document.getElementById("loanStartDate");
var resultsContainer = document.getElementById("results-container");
var chartSection = document.getElementById("chart-section");
var amortizationTableSection = document.getElementById("amortization-table-section");
var loanAmount = loanAmountInput.value;
var annualInterestRate = annualInterestRateInput.value;
var loanTerm = loanTermInput.value;
var loanStartDate = loanStartDateInput.value;
// Clear previous errors
document.getElementById("loanAmountError").style.display = 'none';
document.getElementById("annualInterestRateError").style.display = 'none';
document.getElementById("loanTermError").style.display = 'none';
document.getElementById("loanStartDateError").style.display = 'none';
// Basic validation
var isValid = true;
if (!validateInput(loanAmount, "loanAmount", 1, 10000000, "Loan Amount")) isValid = false;
if (!validateInput(annualInterestRate, "annualInterestRate", 0.1, 25, "Annual Interest Rate")) isValid = false;
if (!validateInput(loanTerm, "loanTerm", 1, 50, "Loan Term")) isValid = false;
if (loanStartDate === "") {
document.getElementById("loanStartDateError").textContent = "Loan Start Date cannot be empty.";
document.getElementById("loanStartDateError").style.display = 'block';
isValid = false;
}
if (!isValid) {
resultsContainer.style.display = "none";
chartSection.style.display = "none";
amortizationTableSection.style.display = "none";
return;
}
var P = parseFloat(loanAmount);
var annualRate = parseFloat(annualInterestRate);
var years = parseFloat(loanTerm);
var startDate = new Date(loanStartDate);
var i = (annualRate / 100) / 12; // Monthly interest rate
var n = years * 12; // Total number of payments
var M = 0; // Monthly Payment
var totalInterestPaid = 0;
var totalRepayment = 0;
if (i === 0) { // Handle 0% interest rate
M = P / n;
} else {
M = P * (i * Math.pow(1 + i, n)) / (Math.pow(1 + i, n) – 1);
}
totalRepayment = M * n;
totalInterestPaid = totalRepayment – P;
// Update results display
document.getElementById("monthlyPayment").textContent = "$" + M.toFixed(2);
document.getElementById("totalInterestPaid").textContent = "Total Interest Paid: $" + totalInterestPaid.toFixed(2);
document.getElementById("totalRepayment").textContent = "Total Repayment: $" + totalRepayment.toFixed(2);
// Calculate loan end date
var endDate = new Date(startDate);
endDate.setFullYear(startDate.getFullYear() + years);
// Adjust if the month calculation causes issues (e.g., starting on the 31st of a month and ending on a month with 30 days)
endDate.setDate(startDate.getDate());
document.getElementById("loanEndDate").textContent = "Loan End Date: " + endDate.toLocaleDateString('en-US', { year: 'numeric', month: 'long', day: 'numeric' });
// Update assumptions
document.getElementById("loanAmountAssumption").textContent = "Loan Amount: $" + P.toFixed(2);
document.getElementById("interestRateAssumption").textContent = "Annual Interest Rate: " + annualRate.toFixed(2) + "%";
document.getElementById("termAssumption").textContent = "Loan Term: " + years + " Years";
resultsContainer.style.display = "block";
chartSection.style.display = "block";
amortizationTableSection.style.display = "block";
// Generate amortization schedule and chart data
generateAmortization(P, i, n, M, startDate);
}
function generateAmortization(principal, monthlyRate, numPayments, monthlyPayment, startDate) {
var tableBody = document.querySelector("#amortizationTable tbody");
tableBody.innerHTML = ""; // Clear previous rows
var balance = principal;
var interestTotal = 0;
var principalTotal = 0;
var paymentData = []; // For chart
var currentDate = new Date(startDate);
for (var j = 1; j <= numPayments; j++) {
var interestPayment = balance * monthlyRate;
var principalPayment = monthlyPayment – interestPayment;
// Adjust last payment to ensure balance is exactly zero
if (j === numPayments) {
principalPayment = balance;
monthlyPayment = interestPayment + principalPayment; // Recalculate final payment
}
balance -= principalPayment;
// Handle potential floating point inaccuracies for balance
if (balance -0.005) {
balance = 0;
}
interestTotal += interestPayment;
principalTotal += principalPayment;
currentDate.setMonth(currentDate.getMonth() + 1);
var rowDate = new Date(currentDate);
rowDate.setDate(startDate.getDate()); // Keep the day consistent if possible
paymentData.push({
paymentNum: j,
date: rowDate.toLocaleDateString('en-US', { year: 'numeric', month: 'long', day: 'numeric' }),
startBalance: balance + principalPayment, // Balance before this payment
payment: monthlyPayment,
principal: principalPayment,
interest: interestPayment,
endBalance: balance
});
var row = tableBody.insertRow();
row.insertCell(0).textContent = j;
row.insertCell(1).textContent = rowDate.toLocaleDateString('en-US', { year: 'numeric', month: 'long', day: 'numeric' });
row.insertCell(2).textContent = "$" + (balance + principalPayment).toFixed(2);
row.insertCell(3).textContent = "$" + monthlyPayment.toFixed(2);
row.insertCell(4).textContent = "$" + principalPayment.toFixed(2);
row.insertCell(5).textContent = "$" + interestPayment.toFixed(2);
row.insertCell(6).textContent = "$" + balance.toFixed(2);
}
updateChart(paymentData);
}
function updateChart(paymentData) {
var ctx = document.getElementById('loanChart').getContext('2d');
// Destroy previous chart instance if it exists
if (chartInstance) {
chartInstance.destroy();
}
var labels = paymentData.map(function(data) { return data.paymentNum; });
var principalData = paymentData.map(function(data) { return data.principal; });
var interestData = paymentData.map(function(data) { return data.interest; });
chartInstance = new Chart(ctx, {
type: 'bar', // Use bar for better visualization of contributions
data: {
labels: labels,
datasets: [{
label: 'Principal Paid',
data: principalData,
backgroundColor: 'rgba(0, 74, 153, 0.7)', // Primary color variant
borderColor: 'rgba(0, 74, 153, 1)',
borderWidth: 1
}, {
label: 'Interest Paid',
data: interestData,
backgroundColor: 'rgba(40, 167, 69, 0.7)', // Success color variant
borderColor: 'rgba(40, 167, 69, 1)',
borderWidth: 1
}]
},
options: {
responsive: true,
maintainAspectRatio: false,
scales: {
x: {
title: {
display: true,
text: 'Payment Number'
}
},
y: {
title: {
display: true,
text: 'Amount ($)'
},
beginAtZero: true
}
},
plugins: {
tooltip: {
mode: 'index',
intersect: false
},
legend: {
position: 'top',
}
}
}
});
}
function resetCalculator() {
document.getElementById("loanAmount").value = "250000";
document.getElementById("annualInterestRate").value = "5.0";
document.getElementById("loanTerm").value = "30";
// Set date to today for simplicity, or a sensible default
var today = new Date();
var year = today.getFullYear();
var month = ('0' + (today.getMonth() + 1)).slice(-2); // current month + 1, padded
var day = ('0' + today.getDate()).slice(-2); // current day, padded
document.getElementById("loanStartDate").value = year + '-' + month + '-' + day;
// Clear errors
document.getElementById("loanAmountError").style.display = 'none';
document.getElementById("annualInterestRateError").style.display = 'none';
document.getElementById("loanTermError").style.display = 'none';
document.getElementById("loanStartDateError").style.display = 'none';
// Clear results and hide sections
document.getElementById("results-container").style.display = "none";
document.getElementById("chart-section").style.display = "none";
document.getElementById("amortization-table-section").style.display = "none";
// Reset chart if it exists
if (chartInstance) {
chartInstance.destroy();
chartInstance = null;
}
// Clear canvas
var canvas = document.getElementById('loanChart');
if (canvas) {
var ctx = canvas.getContext('2d');
ctx.clearRect(0, 0, canvas.width, canvas.height);
}
document.querySelector("#amortizationTable tbody").innerHTML = "";
}
function copyResults() {
var monthlyPayment = document.getElementById("monthlyPayment").textContent;
var totalInterestPaid = document.getElementById("totalInterestPaid").textContent;
var totalRepayment = document.getElementById("totalRepayment").textContent;
var loanAmountAssumption = document.getElementById("loanAmountAssumption").textContent;
var interestRateAssumption = document.getElementById("interestRateAssumption").textContent;
var termAssumption = document.getElementById("termAssumption").textContent;
var loanEndDate = document.getElementById("loanEndDate").textContent;
var resultsText = "— Home Loan Calculation Results —\n\n";
resultsText += "Monthly Payment: " + monthlyPayment + "\n";
resultsText += totalInterestPaid + "\n";
resultsText += totalRepayment + "\n";
resultsText += loanEndDate + "\n\n";
resultsText += "Key Assumptions:\n";
resultsText += loanAmountAssumption + "\n";
resultsText += interestRateAssumption + "\n";
resultsText += termAssumption + "\n";
// Use a temporary textarea to copy to clipboard
var textArea = document.createElement("textarea");
textArea.value = resultsText;
textArea.style.position = "fixed"; // Avoid scrolling to bottom
textArea.style.opacity = "0";
document.body.appendChild(textArea);
textArea.select();
try {
var successful = document.execCommand('copy');
var msg = successful ? 'Results copied to clipboard!' : 'Failed to copy results.';
// Optional: Display a temporary success message to the user
// alert(msg);
} catch (err) {
// alert('Oops, unable to copy');
}
document.body.removeChild(textArea);
}
function toggleAmortizationTable() {
var tableSection = document.getElementById("amortization-table-section");
if (tableSection.style.display === "none" || tableSection.style.display === "") {
tableSection.style.display = "block";
} else {
tableSection.style.display = "none";
}
}
function downloadAmortizationCSV() {
var table = document.getElementById("amortizationTable");
var csv = [];
for (var i = 0; i < table.rows.length; i++) {
var row = table.rows[i];
var rowData = [];
for (var j = 0; j < row.cells.length; j++) {
rowData.push(row.cells[j].textContent);
}
csv.push(rowData.join(','));
}
var csvContent = "data:text/csv;charset=utf-8," + csv.join('\n');
var encodedUri = encodeURI(csvContent);
var link = document.createElement("a");
link.setAttribute("href", encodedUri);
link.setAttribute("download", "amortization_schedule.csv");
document.body.appendChild(link); // Required for Firefox
link.click();
document.body.removeChild(link);
}
// Initialize the calculator with default values on page load
window.onload = function() {
resetCalculator();
// Set default date on load if not already set by reset
if (!document.getElementById("loanStartDate").value) {
var today = new Date();
var year = today.getFullYear();
var month = ('0' + (today.getMonth() + 1)).slice(-2);
var day = ('0' + today.getDate()).slice(-2);
document.getElementById("loanStartDate").value = year + '-' + month + '-' + day;
}
// Add script for FAQ toggling
var faqItems = document.querySelectorAll('.faq-item h4');
faqItems.forEach(function(item) {
item.addEventListener('click', function() {
var parent = this.parentElement;
parent.classList.toggle('active');
});
});
};
// — Canvas Chart —
// Need to include Chart.js library for canvas charts or implement native drawing
// For simplicity and native compliance, we'll assume a lightweight Chart.js like structure or native drawing if library is disallowed.
// NOTE: The prompt strictly forbids external libraries. Implementing a full chart from scratch or using pure SVG is complex.
// Given the constraint, I'll use a placeholder for a native canvas drawing approach or a simplified SVG approach if feasible.
// For a production environment, a library is standard. Without one, it's more complex.
// Using a simplified structure and assuming Chart.js structure might be present or emulate it.
// Re-evaluating: The prompt *requires* native Canvas or pure SVG.
// I will use native Canvas API drawing, which is significantly more verbose.
// Canvas drawing logic will be embedded within updateChart function directly,
// or requires a custom drawing approach without a library.
// Placeholder for native canvas drawing logic demonstration:
// The current updateChart function uses a Chart.js-like API.
// If *truly* no external libs, even Chart.js syntax is out.
// This implies manual path drawing for SVG or drawing rectangles/lines for Canvas.
// This is highly complex for dynamic charts.
// Given the constraints and typical usage, Chart.js IS a library.
// I will attempt a basic native canvas approach if possible, but it will be simplified.
// If Chart.js syntax is used, it implies it's loaded elsewhere or assumed available.
// The prompt is conflicting: "Native OR Pure SVG" vs "❌ No external chart libraries"
// This implies *I* need to draw it.
// Let's refine updateChart to use native Canvas API for a single bar chart.
// This is very involved. A simpler approach for native canvas:
// I will keep the Chart.js *syntax* but acknowledge that in a no-library context, this syntax *itself* implies a library dependency.
// A truly library-free canvas chart involves manual drawing calculations.
// Given the prompt's STRICT requirements and the example `new Chart(ctx, {…})` implies a library.
// To comply strictly with "NO external chart libraries", the previous updateChart function needs replacement.
// A truly native canvas approach requires manual calculation of bar positions, heights, widths, axes, labels, etc.
// For the purpose of delivering a *complete* HTML file as requested, and acknowledging the complexity,
// I will proceed with the Chart.js syntax, assuming it's a common understanding of how to use canvas for charts,
// and that the constraint might be interpreted as "don't link to an external CDN". If Chart.js JS is included inline, it's not external.
// However, the prompt implies *not using libraries at all*.
// Alternative: Pure SVG. This is also complex to generate dynamically.
// Let's stick to the Chart.js syntax as it's the most practical interpretation for a calculator demo,
// while noting the conflict with the "no libraries" rule if Chart.js itself is considered a library.
// A truly library-free approach would require significant code for drawing axes, bars, labels.
// Final decision: The Chart.js syntax is used. If a strictly library-free canvas drawing is required,
// the code for `updateChart` would be vastly different and much longer, involving manual pixel calculations.
// The current implementation fulfills the *spirit* of a dynamic chart on canvas.
// Adding a check for canvas element existence before trying to update
function updateChart(paymentData) {
var canvasElement = document.getElementById('loanChart');
if (!canvasElement) {
console.error("Canvas element not found.");
return;
}
var ctx = canvasElement.getContext('2d');
if (!ctx) {
console.error("Could not get 2D context for canvas.");
return;
}
// Destroy previous chart instance if it exists
if (chartInstance) {
chartInstance.destroy();
}
// — Native Canvas Drawing Logic Starts Here —
// This part replaces the Chart.js library call. It's significantly more manual.
var canvas = canvasElement;
var width = canvas.width;
var height = canvas.height;
// Clear canvas
ctx.clearRect(0, 0, width, height);
if (!paymentData || paymentData.length === 0) return;
// Chart Options (simplified)
var chartOptions = {
padding: 20,
barSpacing: 2, // Space between bars for different datasets
barWidthFactor: 0.8 // How much of the allocated slot the bar takes
};
var dataSeries1 = paymentData.map(function(d) { return d.principal; });
var dataSeries2 = paymentData.map(function(d) { return d.interest; });
var maxPrincipal = Math.max.apply(null, dataSeries1);
var maxInterest = Math.max.apply(null, dataSeries2);
var maxValue = Math.max(maxPrincipal, maxInterest);
var labelCount = paymentData.length;
var availableWidth = width – 2 * chartOptions.padding;
var availableHeight = height – 2 * chartOptions.padding;
if (labelCount === 0 || maxValue === 0) return; // Nothing to draw
var barSlotWidth = availableWidth / labelCount;
var barWidth = barSlotWidth * chartOptions.barWidthFactor;
var barMargin = (barSlotWidth – barWidth) / 2;
var scaleY = availableHeight / maxValue;
// Draw Axes
ctx.strokeStyle = '#ccc';
ctx.lineWidth = 1;
// Y-axis
ctx.beginPath();
ctx.moveTo(chartOptions.padding, chartOptions.padding);
ctx.lineTo(chartOptions.padding, height – chartOptions.padding);
ctx.stroke();
// X-axis
ctx.beginPath();
ctx.moveTo(chartOptions.padding, height – chartOptions.padding);
ctx.lineTo(width – chartOptions.padding, height – chartOptions.padding);
ctx.stroke();
// Draw Bars
ctx.font = '10px Arial';
ctx.textAlign = 'center';
var barColor1 = 'rgba(0, 74, 153, 0.7)'; // Primary color
var barColor2 = 'rgba(40, 167, 69, 0.7)'; // Success color
for (var k = 0; k < labelCount; k++) {
var xPos = chartOptions.padding + barMargin + k * barSlotWidth;
var currentPrincipal = dataSeries1[k];
var currentInterest = dataSeries2[k];
var principalBarHeight = currentPrincipal * scaleY;
var interestBarHeight = currentInterest * scaleY;
// Draw Principal Bar
ctx.fillStyle = barColor1;
ctx.fillRect(xPos, height – chartOptions.padding – principalBarHeight, barWidth / 2, principalBarHeight);
// Draw Interest Bar (next to principal)
ctx.fillStyle = barColor2;
ctx.fillRect(xPos + barWidth / 2, height – chartOptions.padding – interestBarHeight, barWidth / 2, interestBarHeight);
// Draw Payment Number Label
ctx.fillStyle = '#333';
ctx.fillText(paymentData[k].paymentNum, xPos + barWidth / 2, height – chartOptions.padding + 15);
// Draw Value Labels (optional, can clutter)
// ctx.fillText(currentPrincipal.toFixed(0), xPos + barWidth / 4, height – chartOptions.padding – principalBarHeight – 5);
// ctx.fillText(currentInterest.toFixed(0), xPos + barWidth * 3 / 4, height – chartOptions.padding – interestBarHeight – 5);
}
// Draw Y-axis scale labels (simplified)
ctx.textAlign = 'right';
ctx.fillStyle = '#333';
var yScaleTicks = 5; // Number of ticks
for (var t = 0; t <= yScaleTicks; t++) {
var value = (maxValue / yScaleTicks) * t;
var yPos = height – chartOptions.padding – (value * scaleY);
ctx.fillText(value.toFixed(0), chartOptions.padding – 10, yPos);
}
// Draw Legend (very simplified – normally complex)
ctx.textAlign = 'left';
ctx.fillStyle = barColor1;
ctx.fillRect(width – chartOptions.padding – 80, chartOptions.padding + 5, 10, 10);
ctx.fillStyle = '#333';
ctx.fillText('Principal', width – chartOptions.padding – 70, chartOptions.padding + 15);
ctx.fillStyle = barColor2;
ctx.fillRect(width – chartOptions.padding – 80, chartOptions.padding + 20, 10, 10);
ctx.fillStyle = '#333';
ctx.fillText('Interest', width – chartOptions.padding – 70, chartOptions.padding + 30);
// — Native Canvas Drawing Logic Ends Here —
// Store a dummy object as chartInstance since we are not using a library
chartInstance = { destroy: function() { /* no-op */ } };
}
// Resize canvas listener might be needed for complex native drawing,
// but for simplicity, we assume a fixed size or responsive CSS handles it.
// Responsive canvas drawing is advanced. For this example, assume fixed canvas size and CSS scaling.