Simple interest is calculated only on the original principal: SI = P × R × T ÷ 100, where R is the annual rate and T is the time in years. The calculator converts months and days to years and shows the total amount P + SI.
How to calculate simple interest
- Enter the principal and the annual interest rate.
- Enter the time and choose years, months or days.
- Read the interest and total amount with the working.
Simple vs compound interest
With simple interest the interest each year is the same because it is always charged on the original principal. With compound interest, interest is added to the balance and earns interest itself, so the total grows faster. Use the compound interest calculator for savings and investments.
Frequently asked questions
What is the simple interest on 100,000 at 10% for 3 years?
100,000 × 10 × 3 ÷ 100 = 30,000, so the total is 130,000.
How are days converted?
Days are divided by 365.
Updated October 2026 · Built and tested by Sharjeel Tahir · How our tools are tested