Simple Interest Calculator
Calculate simple interest on a principal amount over time.
Interest Earned
Total Amount
Free to useNo software to install — works in any modern browser.
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Works on mobileSame tool on your phone, tablet or desktop.
How it works
- Enter — type or paste your values or text.
- Get the result — it is worked out in your browser.
- Adjust — change the inputs to compare, or copy the result.
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About Simple Interest Calculator
Simple interest is charged or earned only on the original amount, called the principal. The formula is: interest = principal × annual rate × time in years.
An example
On 100,000 at 12% a year for 2 years, the interest is 100,000 × 0.12 × 2 = 24,000, so the total at the end is 124,000. The interest is the same 12,000 each year, because it is always calculated on the original 100,000.
Simple vs compound interest
With compound interest, each year's interest is added to the balance and earns interest itself. The same 100,000 at 12% compounded once a year for 2 years grows to 125,440 — 25,440 of interest instead of 24,000. The gap is small at first and grows quickly over longer periods, which is why savings and investments are usually compared on a compound basis. The Compound Interest Calculator shows the difference for your own numbers.
Where simple interest is used
Short-term personal loans, some car financing, certain fixed deposits that pay interest out rather than adding it back, and many school and exam questions. For loans repaid in equal monthly instalments, banks use a different calculation in which the interest falls as the balance is paid down — use the Loan / EMI Calculator for those.
Getting the time right
The rate is usually per year, so time must be in years too: 6 months is 0.5 and 18 months is 1.5. If a rate is given per month, multiply it by 12 first, or keep everything in months.
For Islamic finance products, which avoid interest altogether, the terms and calculations work differently, so ask the provider how their profit or rental amount is worked out.
An example
On 100,000 at 12% a year for 2 years, the interest is 100,000 × 0.12 × 2 = 24,000, so the total at the end is 124,000. The interest is the same 12,000 each year, because it is always calculated on the original 100,000.
Simple vs compound interest
With compound interest, each year's interest is added to the balance and earns interest itself. The same 100,000 at 12% compounded once a year for 2 years grows to 125,440 — 25,440 of interest instead of 24,000. The gap is small at first and grows quickly over longer periods, which is why savings and investments are usually compared on a compound basis. The Compound Interest Calculator shows the difference for your own numbers.
Where simple interest is used
Short-term personal loans, some car financing, certain fixed deposits that pay interest out rather than adding it back, and many school and exam questions. For loans repaid in equal monthly instalments, banks use a different calculation in which the interest falls as the balance is paid down — use the Loan / EMI Calculator for those.
Getting the time right
The rate is usually per year, so time must be in years too: 6 months is 0.5 and 18 months is 1.5. If a rate is given per month, multiply it by 12 first, or keep everything in months.
For Islamic finance products, which avoid interest altogether, the terms and calculations work differently, so ask the provider how their profit or rental amount is worked out.
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