Free tool
Compound interest calculator
Updated November 6, 2026. Runs entirely in your browser; nothing you type is sent anywhere.
Enter a starting principal, annual rate, years, compounding frequency, and an optional monthly contribution. You'll see a future-value sketch, the interest above what you put in, and a calm sentence for money talks. Simple arithmetic only—not financial or investment advice.
How to use the number
- Treat the rate as a planning assumption, not a promise. Real accounts change rates, fees, and taxes.
- If the monthly contribution is the hard part, free cash by renegotiating bills or unlocking pay—then re-run the math.
- Compare a few rates and timelines rather than trusting one rosy scenario.
- When the hard part is the phone call—a bill, a landlord, a raise, or an offer—use a script, not improvisation under stress.
What to say when cash or pay is the bottleneck
Knowing the future-value sketch is step one. Saying the next line on a bill, rent, raise, or offer call is where people freeze. The Offer Kit ($29) gives word-for-word lines for ask-and-hold pay moments plus Call Mode. If bills are eating the monthly contribution, see the Bills Kit ($19). One-time purchase, 14-day refund on both.
Get the Offer Kit, $29 Get the Bills Kit, $19
What is compound interest?
Compound interest means earnings are added to the balance so later periods earn on both principal and prior earnings. A common sketch uses A = P × (1 + r/n)^(n×t), where P is principal, r is the annual rate as a decimal, n is compounds per year, and t is years.
Is this investment advice?
No. It is simple arithmetic on the numbers you type, plus a sample sentence you can adapt. It is not a savings plan, investment recommendation, tax advice, or substitute for advice from a qualified professional.
What rate should I enter?
Use a rate that matches what you are modeling (for example an advertised APY sketch, or a planning assumption). Real returns, fees, taxes, and inflation change the outcome; this tool only compounds what you enter.
Guidance only, not legal, financial, or tax advice. The calculator does simple arithmetic on the numbers you enter.