Skip to content

Simple interest calculator

Interest on a principal for years, months or days, without compounding.

Reviewed by Victor Yuki Matusita on . First published .

Your numbers stay on your device
$
%
years

Interest

$1,500.00

$10,000.00 at 5% for 3 years earns $1,500.00 of simple interest, for a total of $11,500.00.

  • Principal $10,000 · 87%
  • Interest $1,500 · 13%

Advertisements

Interest for each year

How to use the simple interest calculator

  1. Enter the principal and the yearly rate.
  2. Choose years, months or days and type how long.
  3. Read the interest and the total, and save the table as a PDF or a CSV.

How simple interest is worked out

The formula

I = P × r × t, where P is the principal, r the yearly rate and t the time in years: months ÷ 12, or days ÷ 365. The total is P + I.

Unlike compound interest, the interest does not earn interest, so it grows by the same amount every year.

Assumptions

  • Interest is charged on the principal only, never on earlier interest.
  • A year has 365 days; a month is a twelfth of a year.
  • The interest is rounded to the cent, half up, once, at the end.

Worked example

This is the example the calculator opens with, worked out by the same engine you use above.

You enter
Principal$10,000.00
Yearly rate5%
Time inyears
Time3 years
You get
Interest$1,500.00
Total$11,500.00

$10,000.00 at 5% for 3 years earns $1,500.00 of simple interest, for a total of $11,500.00.

Sources

Educational tool

This calculator is an educational tool, not financial advice. A contract can count days differently, for example with a 360-day year.

Questions about simple interest

What is the difference between simple and compound interest?

Simple interest is charged on the principal only. Compound interest is also charged on the interest already added, so it grows faster over time.

Which loans use simple interest?

Many short loans and some car loans charge interest on what you owe, without adding unpaid interest to the balance. Check how your contract counts it.

Why a 365-day year?

It is the calendar year and the one the calculator declares. Some banks use 360 days, which gives a little more interest for the same number of days.

Can the time be a fraction of a year?

Yes: choose months or days. Eighteen months, for example, is a year and a half.

Privacy

Your numbers stay on your device. The calculator runs in your browser, so nothing you type is sent anywhere, and the link you copy keeps the numbers after the #, a part of the address your browser never sends.