Simple Interest Calculator Online — Free Tool
Instantly calculate simple interest and total accumulated value based on your principal amount, interest rate, and time period.
Simple Interest Calculator
Calculates interest using: Interest = Principal × Rate × Time.
About this tool
The Simple Interest Calculator computes interest using the standard formula: Interest = Principal × Rate × Time. Enter your principal amount, annual interest rate as a percentage, and time period in years — the calculator instantly shows total interest earned and the final accumulated amount.
Unlike compound interest, where interest earns interest on itself, simple interest is calculated only on the original principal. It is used for most short-term personal loans, car loans, and fixed-term savings accounts.
Common use cases
- Calculating total interest on a personal or car loan
- Estimating returns on a fixed-term savings account
- Comparing simple vs compound interest on an investment
- Working out how much interest you will pay on a short-term loan
- Finance homework and exam practice using I = P × R × T
How to use
- Enter the principal — the starting amount (e.g. 10000 for $10,000).
- Enter the annual interest rate as a percentage (e.g. 5 for 5%).
- Enter the time period in years (e.g. 3 for 3 years, or 0.5 for 6 months).
- The calculator instantly shows interest earned, total amount, and a principal/interest breakdown.
This page is available at /tools/simple-interest-calculator/.
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FAQ
What is the simple interest formula?
Simple Interest = Principal × Rate × Time (I = P × R × T), where Rate is a decimal (5% = 0.05) and Time is in years.
What is the difference between simple and compound interest?
Simple interest is calculated only on the original principal. Compound interest is calculated on the principal plus accumulated interest — so interest earns interest over time. For long-term investments, compound interest grows significantly faster.
How do I calculate simple interest for months?
Convert months to a fraction of a year. For 6 months use T = 0.5, for 18 months use T = 1.5. The formula stays the same.
What is a realistic simple interest rate?
Personal loans: 6–36% annually. Car loans: 4–12%. Fixed savings accounts: 2–5%. Always compare APR when comparing loan products.
Want to see how compound interest compares? Try the Compound Interest Calculator.