Compound Interest Calculator

Compound Interest Calculator — Free Investment Growth Calculator

See how your money can grow when the interest you earn starts earning interest of its own. Enter what you're starting with, what you'll add each month, and the rate — and get your projected balance, total contributions, and total interest instantly.

How to Use the Calculator

Fill in the initial amount, the monthly contribution, the expected annual interest rate as a percentage, and the number of years. Then choose how often interest compounds — daily, monthly, quarterly, or annually. The final balance updates as you type, with the total you contributed and the interest earned shown beneath it. Set the monthly contribution to zero to see how a single lump sum grows on its own.

How Compound Interest Works

With simple interest you earn only on your original amount. With compound interest you also earn on the interest already added, so growth speeds up over time. For example, $1,000 with $100 added every month at 7% for 10 years grows to about $19,318 — of which $13,000 is money you put in and $6,318 is interest. Leave it for 20 years and the same plan reaches about $56,131, with $31,131 of it interest. Time does most of the work. A lump sum of $10,000 at 6% for 20 years, compounded annually, reaches about $32,071, compared with $22,000 under simple interest.

As a quick rule of thumb, divide 72 by the annual rate to estimate how many years it takes money to double: at 6%, roughly 12 years.

What the Calculator Assumes

The rate is treated as constant for the whole period, and each monthly contribution is added at the end of the month. Your initial amount compounds at the frequency you choose, while monthly contributions compound monthly. Results are shown in dollars and rounded to the nearest whole number, though the maths works the same for any currency. Real returns vary, and taxes, fees, and inflation aren't included, so treat the result as an estimate rather than a guarantee.

Good Uses for This Tool

Planning long-term savings or retirement contributions, comparing the effect of starting earlier versus contributing more, seeing what a savings account or fixed deposit might be worth, and understanding how compounding frequency changes the outcome.

Is It Actually Private?

Yes. Everything is calculated in your browser — the figures you enter are never sent to a server or stored.