Counting House · room 7
Compound Interest Calculator
Project savings growth with compound interest and contributions.
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Balance Total contributions
| Year | Contributions (cumulative) | Interest (cumulative) | Balance |
|---|
Compound interest formula
Without contributions, an amount P invested at annual rate r, compounded n times per year for t years, grows to:
A = P × (1 + r/n)n·t
Regular contributions are added at the end of every month. To combine monthly deposits with any compounding frequency, the calculator uses the equivalent monthly rate (1 + r/n)n/12 − 1, which gives the same effective annual yield as the chosen compounding schedule. Example: $10,000 at 7% compounded monthly for 20 years becomes about $40,387 — and adding $500 a month brings it to roughly $300,000.
Why does compounding frequency matter so little?
Moving from annual to monthly compounding only raises 7% to an effective 7.23% per year. Time in the market and the contribution amount matter far more — which the chart makes obvious.
This is an illustration with a constant rate; real returns vary and are not guaranteed.