Simple Interest Calculator

Simple Interest Calculator uses I = P times r times t, with the rate as an annual percent, and shows interest plus total. It does not compound.

I equals P times r times t

Three fields: principal, annual rate percent, and years. Interest is principal times rate divided by 100 times years. Total is principal plus interest. The form opens on 5000, 5, and 3, which is interest of 750 and a total of 5750. A blank field or a non-number stops with Enter a valid number. A negative principal or a negative year count stops with Principal and years cannot be negative. A negative rate is allowed by the formula and reduces the total. The rate is a yearly percent, not a monthly rate. Years can be a fraction, and the formula treats that fraction as part of a year. Last checked: October 2026, against simpleInterest.

What simple means here

The interest is not added back into the principal. Year two does not earn interest on year one's interest. That is why a compound calculator is a different page. There is no monthly payment, no APR fee, and no inflation adjustment. Those have their own tools. This page does not look up a live bank rate. You type the percent. It does not withhold tax. The total is principal plus interest in the same units you used for principal. Labels do not add a currency sign. Two years at 5 percent on 5000 is 500 of interest. A method that adds the first year's interest into the principal would come out higher. This form does not do that.

How the default is worked

P is 5000. r is 5 percent, which is 0.05 in the formula. t is 3 years. 5000 times 0.05 is 250 of interest per year. Times 3 years is 750. 5000 plus 750 is 5750. If you change years to 1, interest should fall to 250 and the total to 5250. If you change the rate to 0, interest is 0 and the total equals the principal. If those checks fail, the fields were not the numbers you think. The display uses the shared formatter, so a whole number stays whole.

What the result leaves out

A loan payment that stays flat each month is not simple interest. Use the loan or mortgage tool for that shape, and read that tool's own formula before you trust it. A sale price is the discount tool. A percent change between two numbers is a different calculator. This total is not a quote from a lender. Fees, compounding, and a rate that changes every year are outside the three fields. If the note you are checking says compound, do not use this number. Change the years to 1 on the default principal and rate. Interest should read 250 and the total should read 5250. A zero rate on 5000 for 3 years leaves interest at 0 and the total at 5000. A negative year count stops with Principal and years cannot be negative.