Compound Interest Calculator
See how money grows with compound interest.
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Compound interest pays interest on earlier interest as well as on your original deposit, so growth speeds up the longer money stays invested. This compound interest calculator takes a one-time principal, an annual rate, a period in years and how often interest is added, then shows the maturity amount and the interest earned.
The formula: A = P(1 + r/k)^(k × t)
- P is the Principal you invest once.
- r is the Rate (% p.a.) written as a decimal, so 8% becomes 0.08.
- k is Compounds per year: 1 (yearly, the default), 2 (half-yearly), 4 (quarterly) or 12 (monthly).
- t is Time (years); decimals such as 2.5 are accepted.
Interest earned is simply A minus P. The result box lists the maturity amount, principal, interest earned and a reminder of the compounding you chose.
Same deposit, four compounding choices
₹1,00,000 at 8% for 10 years. For yearly compounding the growth factor is 1.08 raised to the power 10, which is 2.158925, so the deposit becomes ₹2,15,892.50.
| Compounds per year | Maturity amount | Interest earned |
|---|---|---|
| 1 (yearly) | ₹2,15,892.50 | ₹1,15,892.50 |
| 2 (half-yearly) | ₹2,19,112.31 | ₹1,19,112.31 |
| 4 (quarterly) | ₹2,20,803.97 | ₹1,20,803.97 |
| 12 (monthly) | ₹2,21,964.02 | ₹1,21,964.02 |
Monthly beats yearly by ₹6,071.52 over the decade, a real but modest gap; the rate and the number of years matter far more. Simple interest at the same 8% would earn only ₹80,000, so compounding added ₹35,892.50 even at the yearly setting.
Two shortcuts worth remembering
Rule of 72. Divide 72 by the annual rate to estimate the years needed to double your money. At 8% that is 9 years, and the exact figure, 1.08 to the ninth power, is 1.999.
Effective annual rate. (1 + r/k)^k − 1 converts any compounding frequency into a single yearly figure: 8% compounded quarterly is 8.24% a year, and 8% compounded monthly is 8.30%. Use it to compare products that quote the same headline rate with different compounding.
Where you meet compounding in India
- Bank fixed deposits usually compound quarterly; the FD Calculator is preset for that.
- PPF calculates interest monthly but credits it once a year, so the yearly option is the closer match. For a deposit made every year, the PPF Calculator adds each instalment and shows the balance year by year.
- Credit card balances compound against you: a monthly rate of 3% works out to about 42.6% a year.
Limits of this calculator
It handles a single lump sum at a fixed rate. It does not add monthly contributions (use the SIP Calculator for those), deduct tax, allow withdrawals or adjust for inflation, and blank fields are read as zero. Market-linked investments have no fixed rate, so any figure you enter for them is an assumption; for a one-time mutual fund investment, the Lumpsum Calculator works from an expected return and also shows the value after inflation. The output is an estimate for planning, not financial advice.