Simple Interest Calculator
Calculate simple interest and the total amount from a principal, an annual rate and a duration, with the formula shown and fractional durations supported.
Runs in your browser — nothing is uploadedWork out simple interest and see the formula behind it
Enter a principal, an annual rate and a duration in years or months, and get the interest and the total back. The calculation is the textbook one: principal multiplied by rate multiplied by time, divided by 100. Nothing compounds. Figures can be shown in pounds, dollars, euros or rupees, which changes the formatting only and never the arithmetic.
Most savings accounts and many loans compound instead, which produces a larger figure over time. To run the same principal, rate and term with compounding and compare the two answers, use CalcCopilot’s compound interest calculator.
What Simple Interest Calculator gives you
Type or drag
Every input has both a number field and a slider, so you can set a figure exactly or explore a range quickly.
Years or months
Enter the duration in whichever unit the agreement uses; months are converted as a fraction of a year.
Four currencies
GBP, USD, EUR and INR formatting. The maths is identical in every case.
The formula is stated
The page shows exactly what is being calculated, so the result can be checked rather than trusted blindly.
Runs in your browser
The figures you type are not sent anywhere.
How to use Simple Interest Calculator
Enter the principal
The amount borrowed, lent or deposited.
Enter the annual rate
As a percentage per year. Zero is allowed.
Set the duration
In years or months, whichever matches the agreement.
Read the result
The interest and the total, rounded to two decimal places.
Other names for this tool
People also look for this as simple interest formula, interest calculator, SI calculator, flat interest calculator and calculate interest on a loan. It is the same tool on this page.
Limitations
- Simple interest only; it does not model compounding.
Questions about Simple Interest Calculator
Which formula is used?
Interest = principal x annual rate x years / 100, and total = principal + interest. A year is treated as 365 days.
Does it handle a zero rate?
Yes. A zero rate produces zero interest and a total equal to the principal.
What is the simple interest formula?
Principal multiplied by the annual rate multiplied by the time in years, divided by 100. The page states it so you can reproduce the result by hand and confirm it matches the basis your lender or textbook uses.
How is this different from compound interest?
Simple interest is calculated only on the original principal, so nothing accumulates on previously earned interest. Most consumer borrowing compounds, which produces a larger figure — confirm which basis you were quoted before relying on this.
Should I enter a monthly or annual rate?
Annual. Entering a monthly rate as if it were annual understates the interest twelvefold, and it is the single most common way one of these results goes wrong.
Can I enter the duration in months?
Yes, and it is converted as a fraction of a year. Note that a year is treated as 365 days here, while a lender may use a different day-count convention that shifts the figure slightly.
Does choosing a different currency change the answer?
No, only the formatting. The arithmetic is identical whether you display pounds, dollars, euros or rupees, so a figure can be read in whichever currency suits the conversation.
Can I rely on this for a real loan?
Use it to understand the shape of the deal, not as the number you commit to. It is a textbook calculation and is not financial advice, and it excludes fees, charges and any particular lender's rules.