Simple Interest Calculator
Free to use, with no sign up. Your entries stay in this browser; calculations run on your device.
Result
I = P × r × t; balance = P + I. r = annual rate / 100, t = years.
OpenStax Contemporary Mathematics: simple interest
Worked example: $1,000 at 5% for 2 years earns $100 simple interest; the final balance is $1,100.
This is fixed-rate arithmetic. Amounts are USD; fees, withdrawals, changing returns, inflation and taxes are excluded. Money inputs accept up to two decimal places. Results round to cents without rounding intermediate interest. Simple interest applies only to the initial principal.
Arithmetic only; not financial advice.
Related calculators: Compound Interest Calculator, Investment Calculator, CD Calculator.
How to use this tool
Enter principal in USD, annual nominal rate as a percentage, and the term in years. Select Calculate to apply I = Prt.
Frequently asked questions
Is this calculator free and private?
Yes. Arithmetic runs in your browser without uploading your entries or saving them to browser storage.
Does the annual rate mean APY?
The input is a nominal annual rate (APR), not APY. Compound mode shows modeled APY from that rate and compounding frequency; simple mode has no compound APY.
How are recurring contributions timed?
Monthly or yearly contributions apply only to complete contribution periods. Start deposits are at the beginning of each complete period and end deposits at its end. A fractional tail earns interest without a partial deposit. Simple interest and the CD preset have no recurring deposits.