What is the simple interest formula?

Simple interest is calculated as I = P × R × T, where P is the principal, R is the annual interest rate (as a decimal), and T is time in years.

Simple Interest Calculator

Estimate simple interest from principal, rate, and time.

This tool runs in your browser. None of your data is saved or sold.

Principal ($)

Annual rate (%)

Years (years)

Optional fee ($)

About This Calculator

Simple interest doesn't compound — interest is calculated only on the original principal. It's used for some car loans, short-term personal loans, and certain savings bonds. This calculator is also useful for understanding the difference between simple and compound interest on the same balance.

Estimates only — not financial, tax, legal, or investment advice. Verify important results with a qualified professional before making decisions.

interest = principal × rate × time; total value = principal + interest + optional fee; optional fee = entered fee amount