Compound Interest Calculator

Project the growth of an investment with monthly contributions.

100% in your browser · No uploads
Final balance$170,619
Total contributed$70,000
Interest earned$100,619

What this does

Compound Interest Calculator projects the future value of an investment with optional monthly contributions, compound growth, and a fixed annual rate of return. See how much of the final balance is your money vs. interest earned.

When to use it

  • Planning a retirement contribution schedule
  • Modeling how much an emergency fund will grow
  • Comparing the long-term value of different saving rates
  • Deciding between "spend now" and "save now"

Frequently asked

Are results guaranteed?

No. Real returns vary year to year. Use 6-8% for a long-term diversified portfolio (S&P 500 historical average ~10% nominal, ~7% real).

Is the compounding monthly or annual?

Monthly. Contributions are added at the end of each month, then interest compounds on the new balance.