Free Compound Interest Calculator

Your initial investment, monthly contributions, rate and compounding in; total contributed, interest earned and growth year by year out. No signup.

Step 1: Initial investment

Initial investment ($)

Money you have available to invest initially.

Step 2: Contribute

Monthly contribution ($)

Added every month — or negative for a monthly withdrawal.

Length of time (years)

Step 3: Interest rate

Estimated annual interest rate (%)
Interest rate variance range (± %)

See results for rates above and below your estimate.

Step 4: Compound it

Compound frequency

Times per year that interest is compounded.

IN 20 YEARS YOU'LL HAVE
$124,379
At 5%
$95,770
At 9%
$163,623
Total contributed$53,000
Interest earned$71,379
YEAR-BY-YEAR GROWTH
Year 1Year 20

How to use the Compound Interest Calculator

  1. Step 1: enter your initial investment.
  2. Step 2: enter your monthly contribution (negative for a monthly withdrawal) and the length of time in years.
  3. Step 3: enter the estimated annual interest rate and a variance range to see better and worse cases.
  4. Step 4: choose how often interest compounds, then read the year-by-year growth.

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Frequently asked questions

What is compound interest?

Interest earned on your interest. Each period, returns are added to the balance, and the next period earns returns on the bigger balance. Over decades this snowballs — which is why the chart below bends upward instead of climbing in a straight line.

What interest rate should I assume?

A savings account might earn 3–5%; the long-run average for a diversified stock portfolio has historically been around 7–10% before inflation. That is exactly why the variance range exists — look at the low number, not just the high one.

How much does compounding frequency matter?

Less than people think: $10,000 at 7% for 20 years is about $38,700 compounded annually versus $40,500 compounded daily. The rate and the time matter far more than the frequency.

Can I model withdrawals?

Yes — enter a negative monthly contribution to model taking money out each month.