Simple Interest Calculator
Use this simple interest calculator to find the interest and total on any principal. Enter an amount, rate, and term to see flat, non-compounding interest.
What it does
The Simple Interest Calculator shows how much interest a fixed principal earns when interest is charged only on the original amount, never on interest already added. It returns the interest earned and the total amount at the end of the term.
Data sources & parameters
This calculator uses standard financial formulas and runs entirely in your browser. It needs no external rate data — your result is computed only from the values you enter above.
We always strive to use the latest data for every variable so our results and reports are as accurate as possible. Even so, errors are possible — you should not rely on this tool or its report alone, and we accept no liability for any decision made based on it.
The formula
Interest = Principal × Rate ÷ 100 × Years, and Total = Principal + Interest
How it works
The principal is multiplied by the annual rate and the number of years. Because simple interest never compounds, the interest for each year is identical and the total grows in a straight line.
Where it is used
- Working out interest on a short-term or fixed-rate loan
- Checking the return on a bond or note that pays flat interest
- Comparing a simple-interest quote against a compounding one
Worked example
Someone deposits $10,000.00 at 5% for 3 years. The account earns … in flat interest, leaving a total of … at the end of the term.
What the simple interest calculator does
The simple interest calculator shows how much a fixed sum earns, or costs, when interest is charged only on the original amount. You enter the principal, the annual interest rate, and the length of time in years, and the tool returns the interest over the whole term and the total amount you finish with.
Simple interest never pays interest on interest, so the maths stays predictable. It suits short-term loans, fixed-rate notes, and any case where you want a quick figure without compounding.
How simple interest works
The interest is always calculated on the original principal. At a fixed annual rate, the interest earned in year one is the same as in year five or year ten, and the balance climbs in equal steps.
With compounding, each period's interest joins the balance and earns interest of its own, so the total accelerates. With simple interest, the interest never rejoins the principal and growth stays linear. Over a single year the two give the same answer; the gap opens as the term lengthens, which is why simple interest is most common on shorter arrangements.
Double the term and you double the interest. Double the rate and you double the interest. Halve the principal and the interest halves too.
The formula
Interest = Principal x Rate / 100 x Time
The principal is the starting amount, the rate is the annual percentage, and time is the number of years; dividing by 100 turns the percentage into a decimal. The amount you end up with is:
Total = Principal + Interest
A principal of 10,000 at 5% a year over 3 years earns 10,000 x 5 / 100 x 3, or 1,500 in interest, for a total of 11,500.
The three inputs
- The principal is the amount you start with, whether you are lending, saving, or borrowing. Interest scales directly with it.
- The annual rate sets how much interest each year adds. With no compounding, a change in the rate has a direct, proportional effect.
- Time multiplies the annual interest. Each additional year adds the same amount.
How to use the calculator
- Enter the principal, the amount you are starting with.
- Enter the annual interest rate as a percentage.
- Enter the term in years.
The tool displays the interest earned and the total amount, and a chart splits the total into your original principal and the interest added.
Savers can check how much a fixed-rate deposit will pay. Borrowers can see the cost of a simple-interest loan before signing. Anyone comparing offers can line up two quotes on the same basis instead of trusting a headline rate.
Simple interest versus compound interest
Many savings accounts, long-term investments, and credit products use compound interest, where the gap over simple interest grows every year. Using a simple interest figure for something that compounds understates the cost or reward, sometimes by a wide margin over a long term.
As a rule of thumb, simple interest is common on fixed-term loans, car finance, some bonds, and short deposits, while compound interest dominates savings accounts, mortgages, and investment portfolios. Check the product's terms when unsure, and use a compound interest calculator for anything that compounds.
Common mistakes
- Assuming interest compounds when it does not, or the reverse. Confirm which method the product uses.
- Mixing up the time unit. The rate is annual, so the term must be in years; a loan quoted in months needs converting first.
- Ignoring fees. Arrangement fees, insurance, and charges can raise the cost of borrowing well above the headline interest.
Use the calculator to check a lender's quote, to estimate the payout on a fixed deposit, or to get a feel for how interest behaves before moving on to compounding scenarios.
This article is general information only and is not financial advice.
About This Simple Interest Calculator
Use this simple interest calculator to get an instant estimate based on the figures you enter. Adjust the inputs above to match your situation, or browse all our calculators to plan your next step.
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