Compound Interest Calculator

Compound Interest Calculator

Project how savings can grow with recurring contributions and compound returns.

UNDERSTAND THE ANSWER

How is this calculated?

The starting balance and each monthly contribution grow at the assumed monthly rate. Actual investment returns vary and are not guaranteed.

Future value with monthly contributionsFV = P(1 + r)ⁿ + PMT × [((1 + r)ⁿ − 1) ÷ r]

A practical example

$10,000 invested with $500 added monthly for 10 years at an assumed 7% return grows to roughly $107,000.

Assumptions, interpretation and common mistakes

Calculation assumptions

  • The return is constant and compounds monthly.
  • Contributions arrive at the end of each month.
  • Taxes, inflation, fees and market volatility are excluded.

How to interpret the result

  • Projected balance combines deposits and estimated compound growth.
  • Growth share shows how much of the ending balance did not come directly from contributions.
  • Compare conservative and optimistic return assumptions instead of relying on one forecast.

Common mistakes to avoid

  • Treating an assumed investment return as guaranteed.
  • Using a nominal return while interpreting the result as today’s purchasing power.
  • Forgetting expense ratios, taxes or irregular contribution timing.