Compound Interest Calculator

Enter your initial investment amount, your planned monthly contribution, the expected annual interest rate, the number of years you plan to invest, and choose a compounding frequency. The calculator will show you the projected future value, total contributions, interest earned, and effective annual rate.

Experiment with different contribution amounts and time horizons to see how powerful compound interest can be over long periods.

A compound interest calculator helps you project the future value of your savings or investments by accounting for interest earned on both your principal and previously accumulated interest. It is one of the most important tools in personal finance for understanding how wealth grows over time.

Compound interest is the engine behind retirement accounts, index funds, and savings goals. Albert Einstein is often credited with calling it the eighth wonder of the world, and this calculator helps illustrate exactly why.

The compound interest formula for a lump sum is:

FV = P × (1 + r/n)^(n × t)

For regular contributions (future value of an annuity):

FV = PMT × [((1 + r/n)^(n × t) − 1) / (r/n)]

• FV = Future value
• P = Initial principal
• PMT = Contribution per compounding period
• r = Annual interest rate (decimal)
• n = Compounding periods per year
• t = Number of years

Example: Starting with $10,000, contributing $500 monthly at a 7% annual return compounded monthly over 20 years yields a future value of approximately $270,000. Of that total, $130,000 comes from your contributions and roughly $140,000 from compound interest.