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Compound Interest Calculator
See what a starting amount grows into when interest compounds and you add a regular contribution. The year-by-year bars show the balance, not a promise of market returns.
$54,713.58
How to use it
- Enter the starting amount and the annual rate.
- Choose monthly, quarterly, or yearly compounding.
- Add a contribution per period, or leave it at zero.
- Read the future value and the yearly balances.
Formula
FV = P(1+r)^n + PMT × ((1+r)^n − 1) / r
r is the rate per period, n is the number of periods, P is the start, and PMT is the contribution at the end of each period. If r is 0, the future value is P + PMT × n.
$10,000 at 7% with $200 each month
Compounded monthly for 10 years, the balance is about $54,713.58. Part of that is the $24,000 of contributions. The rest is growth on the starting amount and on those contributions.
Compound interest means this period’s interest joins the balance and earns interest next period. With monthly compounding, a 7% annual rate is applied as 7% ÷ 12 each month. Contributions in this calculator are added at the end of each compounding period. Ten thousand dollars at 7% compounded monthly, plus $200 at the end of each month, grows to about $54,713.58 after 10 years. Markets do not pay a flat rate. Use the figure to understand the shape of compounding, then treat any real investment’s return as uncertain.
Questions
How does compound interest work?
Interest is added to the balance, and the next period pays interest on that new total. The longer it runs, the larger each period’s interest becomes.
When is the contribution added?
At the end of each compounding period. Monthly compounding with a monthly contribution adds the money after that month’s interest.
Is this an investment forecast?
No. It assumes the rate you type never changes. Real savings rates and markets move.
Are my numbers uploaded?
No. The projection runs in the browser.