Simple Interest Calculator – I = P × r × t
Compute simple interest and the total amount owed or earned.
- Free
- Instant result
- Private · on-device
- No sign-up
How to use: Enter principal, annual rate and time in years. See interest and total.
How to use the Simple Interest Calculator
Enter the principal (starting amount), the annual interest rate as a percent, and the time in years (decimals allowed, such as 0.5 for six months). The calculator uses I = P × r × t with r as a decimal rate.
Simple interest does not compound: you earn (or pay) interest only on the original principal. That differs from compound interest, where interest is added to the balance and itself earns interest.
Results show total interest and the final amount (principal + interest). Use this for short-term loans, some bonds, or classroom examples. Most modern savings accounts and credit cards use compound interest instead.
Always confirm whether your product quotes a nominal annual rate and whether time should be in years or days (day-count conventions differ). This tool assumes a year-based rate without compounding.
Compare the same inputs in our compound interest and EMI calculators to see how compounding or amortisation changes the cost of borrowing or the growth of savings.
Frequently asked questions
What is the simple interest formula?
I = P × r × t, then total = P + I.
Is mortgage interest simple?
No — mortgages amortize with compound interest each period.
How do I use months?
Convert months to years by dividing by 12.
Simple vs compound — which is larger?
Compound grows faster over long periods at the same nominal rate.