Compound Interest Calculator

Watch interest earn interest — your future balance, contributions and growth.

FREE TOOL · WORKS OFFLINE · NO SIGN-UP

Results update instantly as you type.

Final balance
$0
Total contributions (your money in)
$0
Total interest earned
$0

📈 How to Use This Compound Interest Calculator

  1. 1.Start with what you have. The starting amount can be $0 if you only plan to add money monthly — the contributions will do the work.
  2. 2.Use a realistic rate. Savings accounts might pay 1–5%, while long-run stock market indexes have historically averaged around 7–10% per year before inflation — with plenty of ups and downs along the way.
  3. 3.Extend the years. Compounding is back-loaded: try 10 vs 30 years with the same numbers and notice how much of the growth arrives in the final years.
  4. 4.Add a monthly contribution. Even $100 a month changes the ending balance dramatically over decades, because every contribution starts compounding too.
  5. 5.Remember what is not included. Taxes, fees and inflation reduce real-world returns. Treat the result as a clear projection, not a promise.

❓ FAQ

What is compound interest?

Compound interest is interest earned on both your original money and on the interest it has already earned. Over time this snowball effect makes growth accelerate — the longer the money stays invested, the faster it grows.

How does compounding frequency change the result?

More frequent compounding (monthly or daily instead of yearly) grows your balance slightly faster, because interest starts earning its own interest sooner. The effect is real but usually modest compared with the rate, the time period and your contributions.

What is the Rule of 72?

A quick mental shortcut: divide 72 by your annual interest rate to estimate how many years it takes money to double. At 8% per year, money doubles in about 72 ÷ 8 = 9 years (without contributions or withdrawals).

Is this compound interest calculator free?

Yes — 100% free, no sign-up, no limits. Everything runs in your browser; none of your numbers are uploaded or saved. Results are projections, not a guarantee of future returns.