Compound Interest Calculator

See the power of compounding

Compound interest is the engine of long-term wealth: your money earns returns, and those returns go on to earn returns of their own. The longer you stay invested and the more consistently you contribute, the more dramatic the effect. Use the calculator above to model any starting amount, monthly contribution, rate, and time horizon.

A quick example

Put in $1,000, add $300 a month, and earn 7% a year. After 20 years you'd have contributed $73,000 — but the balance would be roughly $160,000. That extra ~$87,000 is pure compounding. Stretch it to 30 years and the gap grows far wider, because the last years compound on the largest balance.

How to use it

• Start small but start early — time matters more than amount.
• Automate the monthly contribution so it actually happens.
• Keep your rate realistic; a high-yield savings account compounds safely, while investing carries more risk and more potential reward.

Frequently Asked Questions

How is compound interest calculated?

Compound interest is earned on both your original deposit and the interest already added. This calculator compounds monthly: each month it adds your return on the current balance, then your monthly contribution, and repeats.

What return rate should I use?

For a high-yield savings account in 2026, around 4%. For long-term stock-market investing, many people model 6–8% as a rough historical average (not guaranteed). Use a conservative number to avoid over-optimistic projections.

Does this account for taxes or inflation?

No — results are nominal, before taxes and inflation. In a tax-advantaged account like an IRA, growth is sheltered; in a taxable account you would owe tax on gains.