Enter a principal amount, a flat interest rate, and a length of time to calculate simple interest — interest that accrues only on the original principal, never compounding.
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Enter the principal, the annual interest rate, and the length of time in years, months or days. The calculator applies the simple interest formula I = P × R × T and shows both the interest amount and the final total.
Simple interest is calculated only on the original principal for the entire term — it never compounds on previously earned interest. The formula is I = P × R × T, where P is the principal, R is the annual rate as a decimal, and T is the time in years. The total amount owed or earned is A = P + I.
Simple interest is common for short-term loans, certain promissory notes, car loans in some regions, and basic savings illustrations.
Unlike compound interest, simple interest grows in a straight line over time rather than accelerating, since interest is never added back to the principal.
Common questions, answered.
Simple interest is I = P × R × T, where P is the principal, R is the annual interest rate as a decimal, and T is the time in years. The total amount is A = P + I.
Simple interest is always calculated on the original principal only. Compound interest is calculated on the principal plus any interest already earned, so it grows faster over time.
Yes. Choose months or days from the time unit dropdown and the calculator converts it to years automatically (using 30.44 days per month and 365 days per year).
Yes. The same formula applies whether you're calculating interest you'll earn on a deposit or interest you'll owe on a loan.