How to use the compound interest calculator
- Enter your starting amount, optional monthly contribution, rate and number of years.
- Pick how often interest compounds.
- See your future balance, total contributions and interest earned, plus a year-by-year table.
Why compound interest matters
Compound interest is interest earned on both your original money and the interest it has already earned. Over long periods this "interest on interest" snowballs, which is why starting early matters so much. This calculator applies the standard compound-interest formula and adds your regular contributions, compounding at the frequency you choose. Results are estimates — real returns vary and aren't guaranteed.
Benefits
- Projects growth from a starting amount plus regular monthly contributions.
- Choose daily, monthly, quarterly or yearly compounding.
- Splits the total into what you contributed versus interest earned.
- Year-by-year table so you can see the snowball effect.
Limitations to know
- It assumes a constant rate — real investment returns fluctuate.
- It does not account for tax, fees or inflation.
- Projections are estimates, not guaranteed returns.
Common mistakes to avoid
- Using an optimistic rate and treating the result as a promise.
- Forgetting that inflation reduces the real value of a future balance.
- Ignoring fees, which meaningfully reduce long-run growth.
Alternatives
For borrowing rather than saving use the Loan Calculator or Mortgage Calculator.
Last updated: August 2026 · Reviewed by the AI Toolbox editorial team.
Frequently asked questions
What does compounding frequency change?
More frequent compounding earns slightly more, because interest is added to the balance more often.
Are contributions added before or after interest?
This tool adds contributions monthly and compounds at your chosen frequency, a common and realistic approach.
Is this a guaranteed return?
No — it's a projection using a fixed rate. Real investment returns fluctuate.
Is my data saved?
No — everything is calculated in your browser.