Simple Interest Calculator

Calculate simple interest on a principal amount with a fixed rate and time period. Quick and straightforward.

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1. Enter the principal amount you are investing or borrowing. 2. Set the annual interest rate as a percentage. 3. Specify the time period in years, months, or days. 4. View the interest earned and total amount calculated instantly. 5. Click the copy button to copy any result.

About This Tool

The simple interest calculator computes interest earned or owed on a principal amount using a fixed interest rate over a specified time period. Unlike compound interest, simple interest is calculated only on the original principal, making it straightforward to understand and predict.

Simple interest is commonly used for short-term loans, auto loans, and some types of bonds. This calculator lets you determine the total interest earned, the final amount, and breaks down the calculation step by step so you can verify the math yourself.

Use this tool to quickly compare loan offers, estimate interest on short-term deposits, or understand the cost of borrowing. For longer time horizons where interest compounds, consider using the compound interest calculator to see the full picture.

Formula / How It Works

I = P x R x T, where I = interest, P = principal amount, R = annual interest rate (decimal), T = time in years. Total = P + I.

Frequently Asked Questions

Simple interest is a method of calculating interest where the interest charge is based only on the original principal amount. It does not account for interest earned on previously accumulated interest, making it simpler to calculate but resulting in lower total returns compared to compound interest over the same period.
Simple interest is commonly used for short-term loans (such as auto loans), some personal loans, certain bonds, and treasury bills. It is also used in situations where the lending period is short or when the borrower and lender agree to simpler terms.
Multiply the principal (P) by the annual interest rate (R, as a decimal) by the time in years (T). For example, $1,000 at 5% for 3 years: $1,000 x 0.05 x 3 = $150 in interest. The total amount would be $1,150.
Simple interest is calculated only on the original principal, while compound interest is calculated on the principal plus any previously earned interest. Over time, compound interest grows faster because you earn interest on interest.

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