How to use the compound interest calculator
- Enter the starting amount and the interest rate per year.
- Enter the number of years and choose how often interest is compounded: yearly, half-yearly, quarterly, monthly or daily.
- Add a monthly addition if you plan to keep depositing.
- Pick a currency and read the future value, total deposits, interest earned and the effective annual rate. The table shows each year; Download CSV saves it.
The formula
A = P × (1 + r ÷ n)^(n × t)
- P is the starting amount and r is the annual rate as a decimal (8% is 0.08).
- n is how many times a year interest is added and t is the number of years.
With monthly additions the tool converts your compounding choice to an effective monthly rate, i = (1 + r ÷ n)^(n ÷ 12) − 1, then grows the balance month by month: balance = P × (1 + i)^m + PMT × ((1 + i)^m − 1) ÷ i.
Worked example
Deposit 1,00,000 at 8% for 10 years.
- Yearly compounding: 1,00,000 × 1.08^10 = 2,15,892.
- Monthly compounding: 1,00,000 × (1 + 0.08 ÷ 12)^120 = 2,21,964.
- Add 5,000 a month with monthly compounding and the future value becomes 11,36,694, from total deposits of 7,00,000.
The effective annual rate for 8% compounded monthly is 8.3%, which is why the monthly figure is higher.
The rule of 72
Divide 72 by the annual rate to guess how many years money takes to double. At 8% it is about 9 years. That agrees with the table: 1,00,000 reaches 2,00,000 between years 9 and 10.
What compounding teaches
- Time beats size. Starting early with a small sum often outgrows a late, larger one.
- Fees and inflation work the opposite way and cut the real return.
- Compare accounts by effective annual rate, not the headline rate.
Estimates only, not financial advice.
Related tools
For regular market investing, see the SIP calculator. For borrowing costs, use the EMI calculator. To check a percentage quickly, try the percentage calculator. Everything is calculated in your browser.