Compound Interest Calculator
Interest that earns interest. Set the amount, the rate, how long and how often it compounds, and watch the gap against simple interest open up. Nothing is uploaded.
| Year | Interest that year | Balance |
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Each row earns more than the one above it, because the balance it is charged on keeps growing. That curve is the whole point of compounding, and it is why the last few years do most of the work.
How to use it
- Enter the amount you are starting with and the annual rate.
- Set the number of years. This is the input that changes the answer most, so try moving it before you fiddle with anything else.
- Choose how often interest is added. Fixed deposits in India are usually quarterly; savings accounts are often quarterly too; loans are commonly monthly.
The formula
The final amount is A = P (1 + r / n)n t, where r is the yearly rate as a decimal, n is how many times a year interest is added and t is the number of years. Take the principal away from A and what remains is the interest.
The exponent is where the power hides. Time sits up in the exponent while the rate sits down in the brackets, which is why ten extra years changes the answer far more than one extra percent.
Frequency matters less than people think
One hundred thousand rupees at 8% for ten years comes to 215,892 compounded yearly and 221,964 compounded monthly. Switching from monthly to daily adds about another 570. Banks advertise compounding frequency because it sounds like a benefit, but the two inputs that actually decide your outcome are the rate and the number of years.
The rule of 72
Divide 72 by the interest rate and you get roughly the number of years the money takes to double. At 8% that is nine years, and the exact figure this page works out is 9.01. It is a good mental shortcut between about 4% and 15%, and it drifts at the extremes.
A word of caution: this page shows growth before tax and before inflation. Interest on a fixed deposit is taxable, and 8% growth in a year when prices rise 6% is closer to 2% of real gain. Treat the number as arithmetic, not as advice.
Frequently asked questions
What is the compound interest formula?
The final amount equals the principal times one plus the rate divided by the number of compounding periods in a year, all raised to the power of that number times the years. Subtract the principal and what is left is the interest earned.
Does compounding more often make a big difference?
Less than most people expect. At 8 percent for 10 years, 100,000 grows to 215,892 compounded yearly and 221,964 compounded monthly. Moving from monthly to daily adds only about 570 rupees more. The rate and the number of years matter far more than the frequency.
How much more than simple interest is it?
Over one year at yearly compounding, nothing at all - the two are identical. The gap opens slowly and then accelerates, because interest starts earning interest of its own. The third tile on this page shows exactly how much compounding is adding for the figures you entered.
Is anything I type sent anywhere?
No. The arithmetic happens in JavaScript inside your own browser. Nothing is uploaded and nothing is saved - close the tab and it is gone.