Compound Interest Calculator
Compute future value with optional monthly contributions.
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Last updated: 2026-05-31
Inputs
Formula transparency
Source: defaultFV = P · (1 + r/n)^(n·t) + annuity FV
How to use it
- Enter the principal, rate, and number of years.
- Add a monthly contribution to see the annuity effect.
- Choose the compounding frequency.
Example
- 1,000 at 6% for 10 years grows to about 1,790 with no contributions.
What the result means
Future value is what your money grows to; the return is everything above what you put in.
Common mistakes
- Entering a monthly rate as the annual rate.
- Expecting guaranteed returns.
Limitations
- Nominal — ignores inflation and taxes.
- Not investment advice.
Frequently asked
- Compound vs simple interest?
- Simple is on the principal only; compound adds returns back into the principal each period.
- Why factor in inflation?
- To see your real return, not the nominal one. Inflation erodes purchasing power.
- Is the rate fixed or variable?
- We assume a fixed rate for simplicity; real rates can change.
- Are taxes included?
- No, pre-tax and pre-fees. Investment taxes vary by country.
- How do I convert annual to weekly?
- Use the compounding-frequency selector — the math handles it.
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Results are estimates and not professional advice. Verify important decisions with a qualified professional.