Simple Interest Calculator
Compute simple interest the classic way: SI = P × R × T / 100. Enter the principal, annual rate and time in years or months to see the interest, total amount and a per-month breakdown.
How to use the Simple Interest Calculator
Enter the principal — the amount borrowed, lent or invested.
Type the annual interest rate in percent.
Enter the time period and choose years or months.
Read the interest, the total amount payable and the monthly/yearly breakdown.
Frequently asked questions
What is the simple interest formula?
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 amount payable is P + SI.
How do I use months instead of years?
Convert months to years by dividing by 12 — for example 18 months is 1.5 years — then apply SI = P × R × T / 100. The calculator does this for you.
Is my data safe?
Yes. All calculations happen inside your browser; nothing you type is sent to a server.