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Simple Interest Calculator

Calculate simple interest and total amount for any principal, annual rate, and time period.

6.7M usesUpdated · 2026-04-23Runs locally · zero upload

How to use

  1. Enter the principal — the initial amount invested or borrowed.
  2. Enter the annual rate as a percentage (e.g. 5 for 5%).
  3. Enter the time in years. Decimals are accepted (e.g. 1.5 for 18 months).
  4. The interest and total amount update instantly.

Formula

$$I = \frac{P \times R \times T}{100}$$

Where P = principal, R = annual rate (%), T = time (years).

The total repayment or total value is:

$$\text{Total} = P + I$$

Example

A $1,000 deposit at 5% per year for 3 years:

$$I = \frac{1000 \times 5 \times 3}{100} = $150$$

$$\text{Total} = $1,150$$

Frequently asked questions about Simple Interest Calculator

What is simple interest?

Simple interest is calculated only on the original principal — it does not compound. It grows linearly with time.

How is it different from compound interest?

Compound interest earns interest on both the principal and previously earned interest. Simple interest stays proportional to the original amount.

What units should I use for the rate?

Enter the annual interest rate as a percentage. For 5% per year, enter 5. For a monthly rate, multiply by 12 before entering.