Simple Interest Calculator

Calculates simple interest earned or owed on a principal over a fixed time at a stated annual rate.

Total amount = principal plus linear interest growth. Unlike compound interest, each period earns the same dollar amount of interest.

1. Enter principal and annual interest rate.
2. Enter the time period (years, months, or days).
3. View interest earned and total amount.

Simple interest

I = P × r × t · Total = P + I

Source. Interest equals principal times the annual rate times time in years. Months are divided by 12. Days are divided by 365.25. The total is principal plus that interest.

Updated November 1, 2026

$10,000 at 5% simple interest for 3 years earns $1,500 — total $11,500.

• Simple interest is calculated only on the original principal — not on accumulated interest.
• Most savings accounts and loans use compound interest instead.

When is simple interest used instead of compound?

Some short-term loans, bonds, and penalty calculations use simple interest. Most bank savings and mortgages use compound interest.

What's the difference between simple and compound interest?

Simple interest applies only to the starting principal. Compound interest applies to principal plus previously earned interest, so growth accelerates over time.