Compound Interest Calculator

Find out how much your money could grow. Enter your starting amount, regular contributions, interest rate, and time horizon — and see the snowball effect of compound interest year by year.

Your Results

Final balance
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Total invested
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Interest earned
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Year-by-year breakdown

YearBalance at year end

How to use this calculator

  1. Enter the amount you are starting with today.
  2. Add what you will contribute regularly, and choose monthly or yearly.
  3. Enter the annual interest rate you expect (7% is a common long-term assumption for stock market investing).
  4. Choose how many years you will let it grow, then click Calculate.
Try this: Run the same numbers for 10, 20, and 30 years. Notice how the last 10 years add far more than the first 10 — that is compounding doing the heavy lifting.

Frequently asked questions

What is compound interest?

Compound interest is interest earned on both your original money and the interest you have already earned. Over time, this snowball effect makes your money grow much faster than simple interest.

How is compound interest calculated?

Each period, interest is calculated on the current balance, then added to it. With regular contributions, each new deposit also starts earning interest from the month it is added.

Why does starting early matter so much?

Because compounding needs time. Money invested for 30 years usually ends up far ahead of money invested for 20 years, even if the monthly amounts are the same.

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