Compound Interest Calculator

How to Use the Compound Interest Calculator

1. Enter your initial investment.
2. Set your annual interest rate — use 7% for conservative stock market estimates.
3. Choose your compounding frequency — monthly is standard for most accounts.
4. Set the time period — the longer, the more dramatic the compound effect.
5. Add a monthly contribution to see how regular investing accelerates growth.

How Compound Interest Works

Compound interest earns returns on your returns. The key insight: time is the most powerful variable. An investor who starts at 25 ends up dramatically ahead of someone starting at 35, even with the same contributions. Regular contributions amplify the effect — adding $200/month to a 7% account turns $10,000 into roughly $500,000 over 30 years.

The Compound Interest Formula

Where A = final amount, P = principal, r = annual rate, n = compounds per year, t = years, PMT = periodic contribution.

Tips to Maximize Compound Growth

• Start immediately — every year of delay costs exponentially more to catch up.
• Reinvest all dividends — this doubles the compound effect.
• Maximize tax-advantaged accounts first — 401(k) and IRA growth compounds tax-free or tax-deferred.
• Avoid withdrawing early — every dollar pulled out stops compounding permanently.