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About this tool
Solve simple interest, principal, rate or time from the other three, with a yearly table.
This simple interest calculator works in every direction: give it any three of principal, rate, time and interest and it rearranges SI = P × R × T ÷ 100 to solve for the fourth. Time can be entered in years, months or days on either a 365-day or 360-day basis, and the result comes with the rearranged formula, the total amount due and a year-by-year accrual table.
Open Simple Interest Calculator Detailed on AltFTool — it loads instantly in your browser.
Enter the values you already know.
Fine-tune the options to match your scenario.
Read the result and use it in your planning or reporting.
Interest, principal, rate or time — pick the unknown and the formula is rearranged for you.
Years, months, or days on a 365-day or 360-day convention, which lenders often differ on.
Shows interest per year, the running total, and the amount due at the end of each year.
SI = P × R × T ÷ 100, where P is the principal, R is the annual rate in percent and T is the time in years. The total repayable is P + SI.
Simple interest is charged only on the original principal, so the amount earned each year never changes. Compound interest adds earned interest back to the balance, so later years earn more.
A 360-day year makes each day worth slightly more interest than a 365-day year. Money-market and some commercial loans use 360; most retail deposits use 365, so match whichever your agreement states.
Savings accounts and most fixed deposits compound (usually quarterly), while short-tenure deposits under six months and many informal loans are quoted on a simple-interest basis. Check your product's terms — this tool is informational only.
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