Free Simple Interest Calculator (2026)
Interest & SavingsQuickly calculate simple interest earned or owed on a principal amount over a given period at a fixed interest rate.
Simple Interest Result
Total interest
$1,125
Total amount (P + I)
$6,125
Principal
$5,000
Rate applied
7.5%
What is a Simple Interest Calculator?
A simple interest calculator computes the interest earned or owed on a principal amount using a flat rate applied to the original sum — not to accumulated interest. It is the most straightforward interest model and is commonly used for short-term loans, fixed deposits, and treasury bills in [GEO].
How to use this calculator
Enter the principal amount, the annual interest rate, and the time period in years. The calculator returns the total interest, the final amount (principal + interest), and a breakdown of interest per year, month, and day.
Example
$10,000 at 8% simple interest over 3 years earns $2,400 in interest, giving a total maturity amount of $12,400. The interest is $800 per year, $66.67 per month, or $2.19 per day.
Frequently asked questions
When is simple interest used?
Simple interest is used for short-term loans, car loans in some markets, savings bonds, and treasury bills. It is also used to calculate daily interest on some current accounts and mortgages.
Simple vs compound interest — which is better?
For savings, compound interest is better because interest builds on itself. For borrowing, simple interest is cheaper because you only pay interest on the original principal.
Can I calculate simple interest for months or days?
Yes — convert the period to a fraction of a year. 6 months = 0.5 years; 90 days = 90/365 years. Enter the decimal into the time field.
Is simple interest the same as flat rate interest?
Yes — in many markets, 'flat rate' and 'simple interest' are used interchangeably. They both calculate interest on the original principal for the full term.
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