Compound interest calculator
See how a lump sum grows with compound interest over time.
Enter your values and press Calculate. Your inputs stay in the address, so you can switch language or share the link.
Formula
A = P × (1 + r ÷ n)^(n × t)
How it works
Interest is added to the balance n times a year, and later interest is earned on earlier interest. More frequent compounding gives slightly more growth.
Worked example
The same calculation with the default values:
- Starting amount 1,000
- Annual interest rate 5 %
- Years 10
- Times compounded per year 12
- growth = (1 + 5 ÷ 100 ÷ 12)^(12 × 10) = 1.647009
- A = 1,000 × 1.647009 = 1,647.009498
- interest = 1,647.009498 − 1,000 = 647.009498
Result: Final amount: 1,647.01 USD · Interest earned: 647.01 USD
A constant rate is assumed. Real investments vary and returns are not guaranteed; taxes and fees are ignored.
Common mistakes
- Confusing the number of compounding periods per year with the number of years - annual contributions, monthly compounding, and the loan term are three separate numbers that are easy to swap by mistake.
- Forgetting that more frequent compounding (e.g. daily vs annual) gives a slightly higher return for the same stated annual rate, which is why the compounding frequency field matters.
- Assuming the rate entered is guaranteed - this is a projection at a fixed rate, not a forecast of what any real investment will actually return.
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