.ci-calculator-wrapper {
max-width: 800px;
margin: 0 auto;
font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
color: #333;
line-height: 1.6;
}
.ci-calc-box {
background: #f8f9fa;
border: 1px solid #e9ecef;
border-radius: 8px;
padding: 30px;
box-shadow: 0 4px 6px rgba(0,0,0,0.05);
margin-bottom: 40px;
}
.ci-calc-title {
text-align: center;
margin-bottom: 25px;
color: #2c3e50;
font-size: 24px;
font-weight: 700;
}
.ci-input-grid {
display: grid;
grid-template-columns: 1fr 1fr;
gap: 20px;
}
@media (max-width: 600px) {
.ci-input-grid {
grid-template-columns: 1fr;
}
}
.ci-form-group {
margin-bottom: 15px;
}
.ci-label {
display: block;
margin-bottom: 8px;
font-weight: 600;
font-size: 14px;
color: #495057;
}
.ci-input {
width: 100%;
padding: 12px;
border: 1px solid #ced4da;
border-radius: 4px;
font-size: 16px;
box-sizing: border-box;
transition: border-color 0.2s;
}
.ci-input:focus {
border-color: #4a90e2;
outline: none;
}
.ci-select {
width: 100%;
padding: 12px;
border: 1px solid #ced4da;
border-radius: 4px;
font-size: 16px;
background-color: white;
box-sizing: border-box;
}
.ci-btn {
width: 100%;
padding: 15px;
background-color: #2ecc71;
color: white;
border: none;
border-radius: 4px;
font-size: 18px;
font-weight: bold;
cursor: pointer;
transition: background-color 0.2s;
margin-top: 10px;
}
.ci-btn:hover {
background-color: #27ae60;
}
.ci-results {
margin-top: 30px;
padding-top: 20px;
border-top: 2px solid #e9ecef;
display: none;
}
.ci-result-row {
display: flex;
justify-content: space-between;
margin-bottom: 10px;
font-size: 16px;
}
.ci-result-row.main-result {
font-size: 24px;
font-weight: 800;
color: #2c3e50;
margin-top: 15px;
margin-bottom: 0;
}
.ci-result-label {
color: #6c757d;
}
.ci-result-value {
font-weight: 700;
color: #2c3e50;
}
.ci-content h2 {
color: #2c3e50;
margin-top: 40px;
border-bottom: 2px solid #2ecc71;
padding-bottom: 10px;
display: inline-block;
}
.ci-content p {
margin-bottom: 15px;
}
.ci-content ul {
margin-bottom: 20px;
padding-left: 20px;
}
.ci-content li {
margin-bottom: 8px;
}
.error-msg {
color: #e74c3c;
font-size: 14px;
margin-top: 5px;
display: none;
}
function calculateCompoundInterest() {
var principalInput = document.getElementById('ci-principal');
var monthlyInput = document.getElementById('ci-monthly');
var rateInput = document.getElementById('ci-rate');
var yearsInput = document.getElementById('ci-years');
var frequencyInput = document.getElementById('ci-frequency');
var errorMsg = document.getElementById('ci-error');
var resultContainer = document.getElementById('ci-results-container');
// Parse inputs
var P = parseFloat(principalInput.value);
var PMT = parseFloat(monthlyInput.value);
var ratePercent = parseFloat(rateInput.value);
var t = parseFloat(yearsInput.value);
var n = parseInt(frequencyInput.value);
// Validation
if (isNaN(P) || isNaN(PMT) || isNaN(ratePercent) || isNaN(t) || P < 0 || PMT < 0 || ratePercent < 0 || t <= 0) {
errorMsg.style.display = 'block';
resultContainer.style.display = 'none';
return;
}
errorMsg.style.display = 'none';
var r = ratePercent / 100;
var totalMonths = t * 12;
var futureValue = 0;
// Calculation Logic
// A = P(1 + r/n)^(nt) + PMT * [ (1 + r/n)^(nt) – 1 ] / (r/n)
// However, PMT is usually monthly. If compound frequency != monthly, the formula is more complex.
// For simplicity and standard calculator behavior, we assume PMT is added at the end of every month.
// If frequency is Monthly (n=12), the standard annuity formula works perfectly.
// If frequency differs, we iterate month by month for accuracy.
var currentBalance = P;
var totalPrincipal = P;
// Iterative approach for flexibility with monthly contributions vs varying compound frequencies
for (var i = 1; i <= totalMonths; i++) {
// Add monthly contribution
currentBalance += PMT;
totalPrincipal += PMT;
// Apply interest if the current month coincides with a compounding period
// Months per compound period = 12 / n
var monthsPerCompound = 12 / n;
// We treat interest rate as effective per compound period
// Actually, simple iteration is safer:
// Rate per month = r / 12? No, rate is usually quoted annually.
// Standard formula: FV = P * (1 + r/n)^(n*t)
// Let's stick to the standard formula assuming contributions align with compounding for n=12,
// or use a precise loop accumulating interest daily/monthly.
// Let's use the precise loop method:
// Monthly interest factor (simple approx if n=12): (1 + r/12)
// If n=1 (Annual), interest is applied only at month 12, 24, etc.
}
// Re-calculating using the exact formula method for robustness:
// FV of Initial Principal:
var fvPrincipal = P * Math.pow((1 + r/n), (n * t));
// FV of Monthly Contributions:
// Requires converting annual rate to effective monthly rate if n != 12,
// OR assuming contributions compound at the frequency rate.
// Standard approach for these web calculators:
// Assume contributions happen at compound interval if PMT frequency matches compound,
// OR (most common) just iterate monthly and compound when appropriate.
// Let's restart the calculation loop for maximum accuracy:
var balance = P;
var totalContributed = P;
// Loop through every month
for (var month = 1; month every 1 month. n=1 -> every 12 months. n=4 -> every 3 months.
var monthsPerCompound = 12 / n;
if (n >= 12) {
// Monthly or Daily. If Daily, we just use the formula for the month.
// r/12 is strictly true only if n=12.
// If n=365, effective monthly rate is (1 + r/365)^(365/12) – 1.
var effectiveMonthlyRate = Math.pow((1 + r/n), (n/12)) – 1;
balance += balance * effectiveMonthlyRate;
} else {
// Quarterly, Semi, Annual.
// Only apply interest on specific months (3, 6, 9, 12, etc)
if (month % monthsPerCompound === 0) {
var ratePerPeriod = r / n;
// Interest is applied to the balance BEFORE the contributions of this period?
// Or average balance?
// Simple convention: Apply (r/n) to the current balance.
// Note: current balance includes contributions made during non-compounding months.
balance += balance * ratePerPeriod;
}
}
}
// If P was initial, totalContributed includes P + all PMTs.
// Wait, loop added PMT 120 times for 10 years.
// Correct.
var finalValue = balance;
var totalInterest = finalValue – totalContributed;
// Formatting currency
var formatter = new Intl.NumberFormat('en-US', {
style: 'currency',
currency: 'USD',
minimumFractionDigits: 2,
maximumFractionDigits: 2
});
document.getElementById('ci-final-val').innerHTML = formatter.format(finalValue);
document.getElementById('ci-total-contrib').innerHTML = formatter.format(totalContributed);
document.getElementById('ci-interest-earned').innerHTML = formatter.format(totalInterest);
resultContainer.style.display = 'block';
}
Compound Interest Calculator
Monthly
Quarterly
Semi-Annually
Annually
Daily
Please enter valid positive numbers for all fields.
Future Value:
Total Contributions:
Total Interest Earned:
What is Compound Interest?
Compound interest is often referred to as the "eighth wonder of the world." Unlike simple interest, where you only earn returns on your original principal, compound interest allows you to earn interest on the interest you've already accumulated. Over time, this snowball effect can turn modest monthly savings into significant wealth.
For example, investing $5,000 today with a 7% annual return results in much more money after 20 years if the interest is reinvested (compounded) rather than withdrawn.
How to Use This Calculator
This tool helps you project the future value of your investments. Here is how to interpret the fields:
- Initial Investment: The lump sum of money you are starting with today.
- Monthly Contribution: The amount you plan to add to your investment at the end of every month.
- Annual Interest Rate: The expected yearly rate of return (e.g., the historical average of the stock market is roughly 7-10% unadjusted for inflation).
- Investment Period: How many years you plan to let the money grow.
- Compound Frequency: How often the interest is calculated and added back to your balance. "Monthly" is the most common for savings accounts and standard investment projections.
The Compound Interest Formula
While this calculator handles the heavy lifting, the math behind it is based on the following formula for the principal:
A = P(1 + r/n)^(nt)
Where:
- A = the future value of the investment/loan, including interest
- P = the principal investment amount
- r = the annual interest rate (decimal)
- n = the number of times that interest is compounded per unit t
- t = the time the money is invested for in years
When you add monthly contributions (PMT), the calculation becomes a series of annuities added to the compounded principal, significantly accelerating the growth curve.
3 Tips for Maximizing Returns
- Start Early: Time is the most critical factor in compounding. An investment started 10 years earlier requires significantly less capital to reach the same goal.
- Increase Frequency: Compounding monthly usually yields higher returns than compounding annually, as your interest starts earning interest sooner.
- Consistent Contributions: Even small monthly additions (Dollar Cost Averaging) smooth out market volatility and drastically increase the principal base over decades.