Compound Interest Calculator

How to use this calculator

Enter a starting balance, a monthly contribution, an assumed annual return, and the number of years. The calculator compounds monthly and shows an estimated future balance, total contributions, and estimated growth.

When this calculator is useful

• Retirement and brokerage-account planning
• Comparing small versus large monthly contributions
• Showing why starting earlier can matter more than chasing higher returns

Important limitations

Returns are not guaranteed. Taxes, fees, inflation, volatility, and sequence of returns can materially change real results.

For best results, run at least three cases: a conservative case, a middle case, and a stretch case. If a small change in inputs creates a big change in the answer, that is a sign the decision may be sensitive to rates, fees, timing, or market performance.