/* Scoped styles for the calculator to prevent theme conflicts */
.ci-calc-wrapper {
max-width: 800px;
margin: 0 auto;
font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
color: #333;
background: #fff;
border: 1px solid #e0e0e0;
border-radius: 8px;
padding: 30px;
box-shadow: 0 4px 6px rgba(0,0,0,0.05);
}
.ci-calc-wrapper h2 {
text-align: center;
color: #2c3e50;
margin-bottom: 25px;
}
.ci-grid {
display: grid;
grid-template-columns: 1fr 1fr;
gap: 20px;
}
.ci-input-group {
display: flex;
flex-direction: column;
}
.ci-input-group label {
font-weight: 600;
margin-bottom: 8px;
font-size: 14px;
color: #555;
}
.ci-input-wrapper {
position: relative;
}
.ci-input-wrapper input {
width: 100%;
padding: 12px 12px 12px 35px; /* Space for icon */
border: 1px solid #ccc;
border-radius: 4px;
font-size: 16px;
box-sizing: border-box;
}
.ci-input-wrapper.percent input {
padding: 12px 35px 12px 12px;
}
.ci-prefix {
position: absolute;
left: 12px;
top: 50%;
transform: translateY(-50%);
color: #888;
}
.ci-suffix {
position: absolute;
right: 12px;
top: 50%;
transform: translateY(-50%);
color: #888;
}
.ci-full-width {
grid-column: 1 / -1;
}
.ci-btn {
width: 100%;
padding: 15px;
background-color: #27ae60;
color: white;
border: none;
border-radius: 4px;
font-size: 18px;
font-weight: bold;
cursor: pointer;
transition: background-color 0.3s;
margin-top: 10px;
}
.ci-btn:hover {
background-color: #219150;
}
.ci-results {
margin-top: 30px;
padding: 20px;
background-color: #f8f9fa;
border-radius: 6px;
border-left: 5px solid #27ae60;
display: none; /* Hidden by default */
}
.ci-result-row {
display: flex;
justify-content: space-between;
margin-bottom: 10px;
font-size: 16px;
}
.ci-result-row.total {
font-weight: bold;
font-size: 20px;
color: #2c3e50;
border-top: 1px solid #ddd;
padding-top: 10px;
margin-top: 10px;
}
.ci-article {
max-width: 800px;
margin: 40px auto 0;
line-height: 1.6;
color: #444;
}
.ci-article h3 {
color: #2c3e50;
margin-top: 25px;
}
.ci-article ul {
margin-bottom: 20px;
}
@media (max-width: 600px) {
.ci-grid {
grid-template-columns: 1fr;
}
}
Compound Interest Calculator
Future Value:
$0.00
Total Deposits:
$0.00
Total Interest Earned:
$0.00
Maximize Wealth with 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 your interest. This "snowball effect" is the primary engine behind successful long-term investing and wealth accumulation.
How This Calculator Works
This calculator determines the future value of your investments by accounting for both your initial starting balance and regular monthly contributions. The logic assumes that interest is compounded monthly, which aligns with how most high-yield savings accounts and standard investment portfolios calculate growth.
The Formula Used
While the math can get complex with recurring contributions, the core concept relies on the standard Future Value formula adjusted for annuities:
- Principal Growth: The initial amount grows based on the interest rate raised to the power of time.
- Monthly Contributions: Each monthly deposit earns interest for the remaining time it stays in the account.
Real-World Example
Let's look at a realistic scenario:
If you start with $5,000 and contribute $200 every month into an index fund with an average annual return of 7%.
- After 10 years, your total investment (principal + contributions) would be $29,000.
- However, thanks to compound interest, your account value would grow to approximately $44,400.
- That is over $15,000 in "free money" generated purely by interest compounding over time.
Why Start Early?
Time is the most critical factor in compounding. A smaller monthly contribution over 30 years will often outperform a much larger contribution over only 10 years. Use the calculator above to adjust the "Years to Grow" field and witness how extending your timeline exponentially increases your total interest earned.
function calculateCompoundInterest() {
// 1. Get input values by ID
var principalInput = document.getElementById('ci_principal').value;
var monthlyInput = document.getElementById('ci_monthly').value;
var rateInput = document.getElementById('ci_rate').value;
var yearsInput = document.getElementById('ci_years').value;
// 2. Parse values to floats, handling empty inputs as 0
var principal = parseFloat(principalInput);
var monthly = parseFloat(monthlyInput);
var rate = parseFloat(rateInput);
var years = parseFloat(yearsInput);
// 3. Validation: Check for NaN
if (isNaN(principal)) principal = 0;
if (isNaN(monthly)) monthly = 0;
if (isNaN(rate)) rate = 0;
if (isNaN(years)) years = 0;
// 4. Logic Variables
var months = years * 12;
var monthlyRate = (rate / 100) / 12;
var currentBalance = principal;
var totalContributed = principal;
// 5. Calculation Loop (Iterate through every month for accuracy)
for (var i = 0; i < months; i++) {
// Add interest for this month based on previous balance
var interestForMonth = currentBalance * monthlyRate;
currentBalance += interestForMonth;
// Add monthly contribution
currentBalance += monthly;
totalContributed += monthly;
}
// 6. Calculate breakdown metrics
var futureValue = currentBalance;
var totalInterest = futureValue – totalContributed;
// 7. Format formatting function (Currency)
var formatter = new Intl.NumberFormat('en-US', {
style: 'currency',
currency: 'USD',
minimumFractionDigits: 2,
maximumFractionDigits: 2
});
// 8. Update DOM Elements
document.getElementById('ci_final_val').innerHTML = formatter.format(futureValue);
document.getElementById('ci_total_deposits').innerHTML = formatter.format(totalContributed);
document.getElementById('ci_interest_earned').innerHTML = formatter.format(totalInterest);
// 9. Show the result container
document.getElementById('ci_result_container').style.display = 'block';
}