Simple Interest Calculator

Use our Simple Interest Calculator to work out the interest on a loan, a note or savings when interest is charged only on the original amount. Enter any three of principal, interest, annual rate and time, and it finds the fourth.

Simple interest is principal × rate × time: $12,000 at 6.5% for 9 months earns $585, for a total of $12,585. Earlier interest never earns interest of its own, so the balance grows by the same amount every month — $65 here.

Enter the time in years and months, in days, or as two dates, and choose 365 or 360 days in a year, as your contract states: $100,000 at 7% for 90 days is $1,726.03 of interest over 365 days, or $1,750.00 over 360. You can also find the rate — $450 on $15,000 over 18 months is 2% a year — or how long it takes to earn an amount of interest, shown as an end date when you start from a date.

Nothing is paid or added along the way, and fees and taxes aren’t included, so treat the results as an estimate. To see how much more compound interest would earn, use our Simple vs Compound Interest Calculator; for what a loan costs with fees or regular payments, our Borrowing Cost Calculator. To turn a short-period return into a yearly rate, both simple and compounded, use our Annualized Interest Rate Calculator.