Compound interest calculator with regular contributions
See how an amount grows with compound interest and regular contributions, with a year-by-year breakdown and the effective annual rate after compounding.
Runs entirely in your browser — nothing is uploaded.
Sets formatting only.
Calculated period by period, so contributions only earn interest for the time they were actually invested. Real returns are not smooth, and this ignores tax, fees and inflation — all three matter over a decade.
How to use
- Enter the starting amount, rate and term. The rate is the nominal annual figure.
- Add a regular contribution. Set how often you contribute and how often interest compounds — they can differ.
- Read the split. How much you put in versus how much the interest added.
- Open the year-by-year table. To see when interest starts outpacing contributions.
Questions
What does compounding frequency actually change?
More frequent compounding means interest starts earning interest sooner. At 12% nominal, annual compounding gives 12.00% effective, monthly gives 12.68% and daily gives 12.75%. The gap widens with the rate.
Why does this differ from a simple formula?
Because contributions are applied period by period, so each one only earns interest for the time it was actually invested. Closed-form formulas that assume all contributions were present from the start overstate the result.
What is the difference between nominal and effective rate?
Nominal is the headline annual rate before compounding. Effective (APY) is what you actually earn once compounding is included. Comparing a nominal rate to an effective one is not a fair comparison.
Does this account for tax and inflation?
No, and both matter a lot over long periods. At 3% inflation, money halves in real value in about 24 years — so a nominal 5% return is closer to 2% real.