Compound Interest Calculator
Enter a starting amount, an interest rate, a time period and optional monthly contributions to see the final value and the interest earned.
Your details
Result
Final value
92,480
after 20 years
- Total contributed
- 34,000
- Interest earned
- 58,480
Good to know: Interest earns interest, so the longer you leave it, the faster it grows.
Please note: Illustrative estimate based only on the numbers you enter. This is not financial, investment, tax or legal advice and not an offer of any product. Real products have fees, rate changes and rules this tool does not model. Check figures with your lender or a qualified, independent adviser before you decide.
About this tool
Calculate how savings or investments grow with compound interest — used for retirement planning and investment analysis.
Formula
A = P(1 + r/n)^(nt), where P = principal, r = annual rate, n = compounds/year, t = years.
Reference values
- $10,000 at 5% for 10 years = $16,289
- Compounding monthly yields more than annually
- Doubling time ≈ 72 ÷ interest rate
Questions people ask
What is the compound interest formula?
A = P(1 + r/n)^(nt), where P is the starting amount, r the annual rate, n the compounding periods per year and t the years.
How does compounding frequency matter?
More frequent compounding gives slightly more, but the rate and time matter far more.
Do monthly contributions make a big difference?
Yes. Regular deposits add to the base that earns interest.
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How we calculate this
We use the standard published formula or definition for this calculation, and we show the working so you can check it.
Spotted a mistake? Tell us and we'll check it. How we check our calculators