Simple interest calculator

Calculate simple interest or solve for principal, interest rate, or term from the other inputs.

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Use the example values or enter your own measurements.
Calculate, then copy the result or download the available details.

Example

Input

1,000 at 5% for 2 years

Expected result

100 interest; 1,100 total

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Good to know

The calculation runs in your browser. Use consistent units in fields with no explicit unit.

Calculation method

Interest equals principal × periodic rate × number of periods. Convert the term to the same unit as the rate before multiplying. The end balance adds interest to principal.

I=Prt,\qquad A=P+I

Match the term unit to the quoted rate period. For example, 5% per year applied for 24 months uses 2 annual periods.

Use the inverse modes when the end balance is known. A zero rate or zero term can make the inverse problem non-unique.

Calculation mode

Interest and end balance

Principal
Interest rate · %
Rate period · Per year / Per month
Years
Months

Find principal

End balance
Interest rate · %
Rate period · Per year / Per month
Term
Term unit · Years / Months

Find interest rate

Principal
End balance
Term
Term unit · Years / Months
Rate period · Per year / Per month

Find term

Principal
End balance
Interest rate · %
Rate period · Per year / Per month
Term unit · Years / Months