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Compound Interest Calculator

Watch small monthly deposits turn into serious money.

Compound interest is the engine of long-term wealth: returns earn returns, and the curve bends upward over time. This calculator projects an initial deposit plus optional monthly contributions at a fixed annual rate, compounded monthly, and shows the growth schedule year by year — including how much of the final balance is your contributions versus growth.

Why people use this

People use this to make abstract saving goals visceral: what does $300 a month actually become? It is the calculator financial advisors show clients to end the "I'll start next year" debate, and the one that convinces 25-year-olds that starting now matters more than starting big.

How it works

1. Enter your starting amount (can be $0).
2. Enter a monthly contribution (can be $0).
3. Set an annual return rate — 7% is a common long-run stock-market assumption after inflation; 4–5% for bonds or high-yield savings.
4. Set the number of years. Compounding is monthly.
5. Review the final balance, total contributed, and total growth, plus the year-by-year table.

Common questions

What is the rule of 72?

Divide 72 by your annual return rate to estimate years to double your money. At 7%, money doubles roughly every 10.3 years. This calculator shows the exact curve instead of the estimate.

How much do monthly contributions matter?

Enormously. $500/month at 7% for 30 years grows to about $610,000, of which only $180,000 is your contributions — the remaining $430,000 is growth. Starting 10 years earlier roughly doubles the outcome.

Is a fixed return rate realistic?

Real markets are volatile; a fixed rate is a planning simplification. It is useful for comparing scenarios (rate, contribution, time), not for predicting any specific year.

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