Compound Interest Calculator

Estimate how a starting amount grows when interest is reinvested and optional monthly contributions are added. The calculator uses starting amount, annual rate, years, monthly contribution, and compounding frequency to show future balance, interest earned, and total contributed.

How to use this calculator

Enter the starting amount, annual interest rate, years, optional monthly contribution, and compounding frequency. Use it for savings, CD-style growth, or educational investment scenarios. For contribution plans with inflation adjustment, see the compound growth calculator. For fixed periodic payments, try the future value of annuity calculator.

How compound interest works

With simple interest, interest is calculated only on the original principal. With compound interest, each period’s interest becomes part of the balance, so future interest is calculated on a larger amount.

A basic compound interest formula is:

Future value = Principal x (1 + rate / periods) ^ (periods x years)

If you also make regular deposits, those contributions add their own growth depending on when they are made.

Example

A 10,000 dollar starting balance, 200 dollars added monthly, 7 percent annual interest, 10 years, and monthly compounding grows to about 58,429 dollars. Contributions total 34,000 dollars, so the rest is estimated interest.

Interpreting the result

Time and consistency are powerful inputs. Increasing the monthly contribution or extending the years can matter as much as a small rate change. For basic non-compounding rate math, use the interest calculator. These projections are hypothetical and do not include taxes, fees, or market volatility.