Total Principal: $0.00
Total Interest Earned: $0.00
Total Contributions: $0.00
Understanding Weekly Compound Interest
Compound interest is the interest calculated on the initial principal and also on the accumulated interest of previous periods. It's often referred to as "interest on interest" and is a powerful tool for wealth growth over time. While many calculators focus on monthly or annual compounding, this calculator specifically models weekly compounding, which can lead to slightly faster growth due to more frequent interest application.
The Math Behind Weekly Compounding
The formula for compound interest can be adapted for weekly compounding. The standard formula is:
A = P (1 + r/n)^(nt)
Where:
A = the future value of the investment/loan, including interest
P = the principal investment amount (the initial deposit or loan amount)
r = the annual interest rate (as a decimal)
n = the number of times that interest is compounded per year
t = the number of years the money is invested or borrowed for
For a weekly compounding calculator that also includes regular deposits, the calculation becomes more complex and is typically solved iteratively or using specific financial functions. This calculator uses an iterative approach to sum up the principal, the regular deposits, and the compounded interest weekly.
For each week, the balance is updated as: balance = (previous_balance + weekly_deposit) * (1 + weekly_rate)
Our calculator simulates this week by week to accurately reflect the growth with regular contributions.
Why Use a Weekly Compound Interest Calculator?
Maximizing Growth: Compounding more frequently (weekly vs. monthly or annually) can slightly enhance returns over the long term, assuming the interest rate is applied consistently.
Budgeting and Saving: It helps visualize how consistent, smaller savings deposited weekly can grow into substantial amounts.
Financial Planning: Essential for long-term goals like retirement, down payments, or education funds. Understanding the power of compounding can be highly motivating.
Comparing Investments: Allows users to compare different investment scenarios by varying the initial deposit, weekly contributions, interest rate, and duration.
This calculator provides a clear and concise way to estimate the future value of your investments with weekly compounding and contributions.
function calculateCompoundInterest() {
var principal = parseFloat(document.getElementById("principal").value);
var weeklyDeposit = parseFloat(document.getElementById("weeklyDeposit").value);
var annualRate = parseFloat(document.getElementById("annualRate").value);
var years = parseInt(document.getElementById("years").value);
var resultValueElement = document.getElementById("result-value");
var resultDetailsElement = document.getElementById("result-details");
if (isNaN(principal) || isNaN(weeklyDeposit) || isNaN(annualRate) || isNaN(years) ||
principal < 0 || weeklyDeposit < 0 || annualRate < 0 || years <= 0) {
resultValueElement.textContent = "Invalid Input";
resultDetailsElement.innerHTML = "Please enter valid positive numbers for all fields.";
return;
}
var weeklyRate = annualRate / 100 / 52;
var numberOfWeeks = years * 52;
var totalContributions = principal + (weeklyDeposit * numberOfWeeks);
var futureValue = principal;
var totalInterest = 0;
for (var i = 0; i < numberOfWeeks; i++) {
var interestForWeek = (futureValue + weeklyDeposit) * weeklyRate;
futureValue = futureValue + weeklyDeposit + interestForWeek;
totalInterest += interestForWeek;
}
// Ensure we don't display NaN if calculations yield strange results due to extreme inputs
if (isNaN(futureValue) || !isFinite(futureValue)) {
resultValueElement.textContent = "Error";
resultDetailsElement.innerHTML = "Calculation resulted in an error. Please check inputs.";
return;
}
// Round to two decimal places for currency
var formattedFutureValue = futureValue.toFixed(2);
var formattedTotalInterest = totalInterest.toFixed(2);
var formattedTotalContributions = totalContributions.toFixed(2);
resultValueElement.textContent = "$" + formattedFutureValue;
resultDetailsElement.innerHTML =
"Total Principal: $" + principal.toFixed(2) + "" +
"Total Interest Earned: $" + formattedTotalInterest + "" +
"Total Contributions: $" + formattedTotalContributions;
}