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Simple Interest Calculator
Free simple interest calculator. Calculate interest, principal, rate, or time with I = Prt.
Simple interest is charged on the original principal only. Loans and savings that compound will differ — use the compound interest calculator for those.
Frequently Asked Questions
What is the simple interest formula?
Interest equals principal times rate times time, written I = P × r × t, with the rate as a decimal and time in years. On $10,000 at 5% for 3 years that is $1,500 in interest.
How is simple interest different from compound interest?
Simple interest is charged only on the original principal, while compound interest is charged on principal plus accumulated interest. Over long periods compounding produces noticeably larger totals.
Where is simple interest actually used?
It shows up in many car loans, short-term personal and payday loans, some bonds and Treasury coupons, and court-awarded interest. Most savings accounts and credit cards compound instead.
Can I solve for the rate or the time?
Yes. The calculator rearranges the formula, so entering any three of principal, rate, time, and interest solves for the fourth.