Compound Interest Calculator
See how your savings grow with compound interest. Calculate the future value of an initial deposit plus monthly contributions at any interest rate.
How it works
Compound interest formula
A = P × (1 + r/n)^(n × t) P = initial deposit r = annual interest rate (decimal) n = compounding periods per year t = time in years
Compound interest means you earn interest on your interest. Each period, interest is added to the balance, and the next period's interest is calculated on that larger balance. More frequent compounding and more time both increase growth — time is by far the most powerful factor.
Worked example
A $10,000 deposit at 7% compounded monthly for 20 years grows to about $40,387 with no contributions. Adding $250 per month grows the total to about $170,619 — of which $70,000 is contributions and the rest is interest.
Frequently asked questions
What is the difference between simple and compound interest?
Simple interest is earned only on the original principal. Compound interest is earned on the principal plus all previously earned interest, which makes balances grow faster over time.
How much does compounding frequency matter?
More frequent compounding gives slightly higher returns, but the effect is small compared to the interest rate and time period. Going from annual to monthly compounding on 7% adds about 0.23 percentage points of effective annual yield.
Are taxes and inflation included?
No. Results are pre-tax nominal values. Taxes on interest and the effect of inflation will reduce your real purchasing power.