Compound Interest Calculator
See how your savings grow with compound interest and regular contributions.
Enter your principal, annual interest rate, number of years, optional periodic contribution, and choose how often interest compounds.
Formula & methodology
FV = P(1 + r/n)^(nt) + C · (((1 + r/n)^(nt) − 1) / (r/n)), where P is principal, r the annual rate, n the compounds per year, t the years, and C the contribution per period.
Contributions are treated as an ordinary annuity (added at the end of each compounding period). All math runs locally in your browser.
Worked example
- $1,000 at 5% for 10 years, compounded monthly, no contributions → ≈ $1,647.01 future value — 1000 × (1 + 0.05/12)^(12×10).
Assumptions
- The interest rate stays constant for the whole period.
- Contributions occur at the end of each compounding period.
- Taxes, fees, and inflation are not deducted.
Common mistakes
- Confusing the nominal annual rate with the effective annual rate.
- Entering a monthly rate where an annual rate is expected.
Frequently asked questions
What is compound interest?
Compound interest is interest calculated on both the initial principal and the accumulated interest from previous periods, so growth accelerates over time.
How does compounding frequency affect results?
More frequent compounding (e.g. monthly vs annually) slightly increases the future value because interest is added and re-invested more often.
Privacy
All processing happens locally in your browser. Your data is never uploaded.
Disclaimer: This tool provides estimates for educational purposes only and is not financial advice.
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