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.
Investment Details
What Is Compound Interest?
Compound interest is interest calculated on both the original principal and the accumulated interest from previous periods. In simple terms, it's "interest on interest."
Example: $100 invested at 10% annual interest
Year 1: $100 → $110
Year 2: $110 → $121
Year 3: $121 → $133.10
Instead of growing linearly, your money grows exponentially — this is the key power of compound interest.
The Formula
A = P(1 + r/n)^(nt)
Why It Matters: Everyday Impact
Compound interest can work for you or against you:
When Saving / Investing
- Wealth grows faster over time
- Early investing has huge advantages
When Borrowing
- Debt can grow quickly
- Especially dangerous on credit cards
Albert Einstein is often quoted as calling compound interest:
"The eighth wonder of the world."
Small amounts + time = massive growth.
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
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FAQ
Common questions about Compound Interest Calculator
How we calculate this
We use the standard published formula for this calculation, and we show the working so you can check it.
Spotted a mistake? Tell us and we'll check it within a few days. See how we check our calculators.
Financial disclaimer
Results are estimates based on the numbers you enter. Real products have fees, rate changes and rules this tool does not model. Check figures with your lender or a qualified adviser before you decide.