Simple Interest Calculator

Enter an amount, a yearly interest rate and a length of time to see the interest and the total. Choose years, months or days. Everything works in your browser.

Amount (principal)

Interest rate per year

Time

Unit

Interest earned

$675.00

$5,000.00 at 4.5% a year for 3 years earns $675.00, so the total is $5,675.00.

Total amount: $5,675.00
Interest per year: $225.00
Interest per month: $18.75
Time in years: 3

The simple interest formula

Simple interest is worked out only on the original amount, called the principal. Interest = principal × rate × time, where the rate is the yearly percentage written as a decimal and the time is in years. The total is the principal plus the interest.

Examples on $1,000

Interest earned on $1,000 at different yearly rates and lengths of time.

Rate	1 year	3 years	5 years
3%	$30	$90	$150
5%	$50	$150	$250
8%	$80	$240	$400

Simple versus compound interest

With simple interest the amount of interest is the same every year. With compound interest, interest is added to the balance and then earns interest itself, so it grows faster the longer the money is left. Short personal loans and some bonds use simple interest, while most savings accounts, credit cards and mortgages use compound interest.

Months and days

If the time is not a whole number of years, it is converted: months divided by 12, days divided by 365. Lenders can use other day-count rules, such as 360 days in a year, so a real loan statement may differ by a few cents.

How to calculate simple interest in Excel or Google Sheets

With the principal in A1, the yearly rate in B1 (for example 5%) and the years in C1, use =A1*B1*C1 for the interest and =A1+A1*B1*C1 for the total.

How to use the Simple Interest Calculator tool

Type the amount (the principal).
Type the interest rate per year.
Enter the time and choose years, months or days.
Read the interest, the total amount and the interest per year and per month.

Frequently asked questions

What is the simple interest formula?

Interest = principal × rate × time, with the rate as a decimal and the time in years. $1,000 at 5% for 3 years earns 1,000 × 0.05 × 3 = $150, for a total of $1,150.

What is the difference between simple and compound interest?

Simple interest is calculated only on the original amount. Compound interest is calculated on the amount plus the interest already added, so it grows faster over time. Many savings accounts and loans use compound interest.

How are months and days converted?

Months are treated as one twelfth of a year and days as one 365th of a year. Six months is 0.5 years and 90 days is about 0.247 years.

Is this calculator financial advice?

No. It shows a general calculation only. Real loans and accounts may add fees, compounding or different day-count rules, so check the terms from your lender or bank.