How compound interest works

The basic idea

With a starting balance, a constant rate and regular contributions, each compounding period updates the balance before the next period begins.

Contributions matter

Regular contributions can become a large part of the final amount, especially over longer periods. A useful calculator separates the total you contribute from the estimated interest so the sources of growth are easy to see.

Rates are assumptions

A compound-interest calculator is a scenario model when the rate is entered by the user. Real savings and investment products can have changing rates, fees, taxes and different contribution timing.

Use scenarios

Try different rates, contribution amounts and time periods to understand sensitivity rather than treating one result as a guaranteed future value.

The calculator uses a standard compound-growth model with recurring contributions made once per compounding period. It is a mathematical estimate, not a forecast or investment recommendation.

Related calculators

Information on this page is general and educational. Check the actual terms, rates and rules that apply to you.