Calculator

Compound Interest Calculator

See how a starting amount plus regular monthly contributions grows with compounding.

Future value
$300,851
after 20 years at 7% / year
Total contributed
$130,000
Interest earned
$170,851
Educational and informational only — not financial advice or a recommendation. Results are hypothetical illustrations based on the inputs and a fixed assumed return; real returns vary and you can lose money.

How compounding builds wealth

The earlier you start and the longer you stay invested, the more of your final balance comes from growth rather than your own contributions. Small, consistent monthly contributions often matter more than a large one-off amount, because each contribution has more time to compound.

Tips to get the most from compounding

Contribute regularly, keep costs low (fees compound against you), reinvest any income, and avoid interrupting the compounding by selling during downturns. Use the calculator to compare scenarios — for example, what an extra $100/month does over 20 years.

Frequently asked questions

What is compound interest?

Compound interest is interest earned on both your original money and the interest it has already earned. Over time this compounding effect accelerates growth.

How is it calculated?

This calculator compounds monthly: FV = P(1+r)ⁿ + C·[((1+r)ⁿ − 1) / r], where P is the starting amount, C the monthly contribution, r the monthly rate, and n the number of months.

What return should I assume?

Returns vary and are never guaranteed. Many people use a long-run assumption for diversified portfolios, but actual results differ and you can lose money. This is an illustration, not a prediction.

Want this applied to your real portfolio? Launch the app to set goals and track progress, or read our getting-started guide.