How Simple Interest Calculator Works
Simple interest is calculated only on the original principal, so it grows by the same fixed amount every period rather than compounding. The formula is SI = P × rate × time ÷ 100, and the total payable is the principal plus that interest.
How to Use This Tool
- Enter the principal amount you're lending, borrowing or investing.
- Enter the annual interest rate as a percentage.
- Enter the time period in years (decimals like 2.5 are fine).
- Select Calculate to see the interest earned and the total payable.
Example
A principal of $5,000 at 5% annual simple interest for 3 years earns 5000 × 5 × 3 ÷ 100 = $750 in interest, for a total payable of $5,750.
Helpful Tips
- Simple interest grows linearly — unlike compound interest, it never earns interest on previously earned interest.
- For a rate given per month rather than per year, convert it to an annual rate first (multiply by 12) before entering it.
- Simple interest is common for short-term loans and some bonds; savings accounts and investments more often use compound interest.
Frequently Asked Questions
How is simple interest different from compound interest?
Simple interest is calculated only on the original principal each period. Compound interest is recalculated on the growing balance, including previously earned interest, so it grows faster over time.
Can I enter a time period in months instead of years?
Enter the time in years — for months, divide by 12 first (for example, 6 months is 0.5 years).
Does the rate need to be an annual rate?
Yes, enter the interest rate as an annual percentage; the calculator multiplies it by the number of years you enter.
What does the total payable figure represent?
It's the principal plus the interest earned — the full amount due at the end of the term.
This tool runs entirely in your browser. Your input is not uploaded to any server.