Compound Interest Calculator

See how savings and investments grow with compound interest over time.

See How Your Money Can Grow

This compound interest calculator shows how an initial amount plus regular monthly contributions can grow over time. Enter your starting balance, how much you add each month, an expected annual return and the number of years to see your projected future balance, how much you contributed and how much of the growth came from compounding. It runs in your browser, so your figures stay private.

What compounding does

Compound interest is interest earned on both your original money and the interest it has already earned. Over long periods this snowball effect becomes powerful, which is why starting early matters more than starting big. A modest monthly contribution left to compound for decades can outgrow a much larger sum invested late.

The rule of 72

A quick way to estimate growth is the rule of 72: divide 72 by your annual return to approximate the number of years it takes money to double. At a 7 percent return, money roughly doubles every ten years. Use it as a sanity check alongside the exact figures here.

Things to remember

  • Returns are not guaranteed and vary year to year, so treat the result as a projection.
  • Inflation reduces future buying power, so real growth is lower than the headline number.
  • Consistency wins — regular contributions through ups and downs usually beat trying to time the market.

Estimates only — not financial advice. Investment returns are uncertain and past performance does not predict future results.

Frequently asked questions

What is compound interest?

It is interest earned on both your original money and the interest it has already earned, which makes balances grow faster over time.

How is the future balance calculated?

The calculator compounds your balance monthly and adds your monthly contribution, using your expected annual return over the number of years you set.

What return should I assume?

That depends on where the money is invested and is never guaranteed. Many people use a conservative long-term estimate and treat the result as a projection.

Does this account for inflation?

No. The figure is in todays dollars before inflation, which reduces future buying power.