Simple Interest Calculator

About this simple interest calculator

Simple interest is charged only on the original principal, never on accumulated interest. It is used for many short-term loans, some car loans, bonds' coupon payments and classroom finance problems. Because it doesn't compound, it grows in a straight line: double the time and you double the interest.

Enter the principal, the annual rate and the time in years, months or days, and the calculator returns the interest and the total amount (principal plus interest).

How to use the Simple Interest Calculator

1. Enter the principal amount.
2. Enter the annual interest rate as a percentage.
3. Enter the time and select years, months or days.
4. Read the interest and total amount.

The simple interest formula

I = P × R × T   and   A = P + I

P is the principal, R the annual rate as a decimal and T the time in years. Months are divided by 12 and days by 365 to convert them to years.

Worked example

$5,000 at 5% for 3 years earns 5,000 × 0.05 × 3 = $750 interest, for a total of $5,750. With yearly compound interest the same deposit would earn about $788.

Tips for better results

• For savings accounts and most investments, use the compound interest calculator instead.
• Some lenders use a 360-day year for day counts, which slightly increases the interest.

Frequently asked questions

This calculator provides estimates for planning only and is not financial advice. Confirm exact figures with your lender or a licensed professional.

Last reviewed: October 2026 · Results are calculated in your browser.