Simple Interest Calculator

What Is a Simple Interest Calculator?

A simple interest calculator calculates the interest earned on an original principal amount without adding previously earned interest to the principal. It can be used to quickly determine how much interest will accumulate over a specified period and the resulting total amount.

Simple interest is commonly used for certain loans, financial calculations and other situations where interest is calculated directly from the original principal. Enter the amount, annual interest rate and time period to calculate the result.

Why Use a Simple Interest Calculator?

Calculating simple interest manually is straightforward, but an online calculator can reduce arithmetic errors and make it easier to compare different amounts, rates and time periods.

How to Use the Simple Interest Calculator

Enter the figures you want to calculate and the tool will determine the simple interest and final amount.

1. Enter the principal amount — Enter the original amount on which interest will be calculated.
2. Enter the annual interest rate — Enter the applicable annual interest rate as a percentage.
3. Enter the time period — Enter the length of time and choose whether it is measured in years, months or days.
4. Calculate the result — Select a currency and click Calculate Simple Interest to view the interest earned and final amount.

How to Calculate Simple Interest

The standard simple interest formula is I = P × R × T. In this formula, I represents the interest, P represents the principal, R represents the annual interest rate as a decimal and T represents the time period in years.

For example, if you invest £10,000 at an annual simple interest rate of 5% for 3 years, the interest is £10,000 × 0.05 × 3, which equals £1,500. The resulting total amount is therefore £11,500.

Simple Interest on Different Time Periods

Simple interest can be calculated for periods shorter or longer than one year. When a period is entered in months, it is converted to a fraction of a year. For example, 6 months represents 0.5 years. Days are similarly converted using a 365-day year for this calculator.

Simple Interest vs Compound Interest

The main difference between simple and compound interest is the balance used to calculate future interest. Simple interest uses the original principal throughout the calculation, while compound interest can include previously earned interest in subsequent calculations.

Understanding Your Simple Interest Results

The interest earned is the additional amount generated from the principal at the specified annual rate for the selected period. The final amount is the original principal plus the interest earned.

The calculator assumes that the annual interest rate remains constant and that interest is calculated using the standard simple interest formula. It does not account for fees, taxes, inflation, changing rates or financial product-specific calculation rules.

The currency selector changes the formatting of monetary results only. It does not convert an amount between currencies or use live exchange rates.

Frequently Asked Questions