Your inputs

Interest without compounding

Principal

The starting amount, from $0 through $1 trillion.

Annual interest rate

The simple annual rate, from 0% through 1000%.

Term

Decimals allowed, such as 2.5, from 0 through 200 years.

Your inputs are calculated locally and are not stored.

Balance with interest$11,500.00

$10,000.00 grows by $1,500.00 in simple interest over the term.

Interest earned: $1,500.00
Principal: $10,000.00

Formula & methodology

How simple interest is calculated

Simple interest is charged only on the original principal — it does not build on previously earned interest. Multiply the principal by the annual rate and the number of years to get the total interest, then add it back to the principal for the final balance.

Interest = Principal × Rate × Years
Total = Principal + Interest

Principal: The starting amount
Rate: Annual interest rate, as a decimal
Years: The term, can be fractional

Worked example

$10,000 at 5% for 3 years

With a $10,000 principal, a 5% annual rate, and a 3-year term, the interest is $10,000 × 0.05 × 3 = $1,500. Adding that to the principal gives a total balance of $11,500. Because there is no compounding, the same $500 of interest is earned each year.

This is an educational calculation based only on the values you provide, and it is not financial advice.

Assumptions

What this calculator assumes

Interest is simple, never compounded on prior interest.
The rate stays constant across the whole term you enter.
No deposits, withdrawals, fees, or taxes are modeled.
Money values are rounded to the nearest cent for display.

Common questions

Simple interest FAQ

Can I enter the period in months, days, or exact dates?

Yes. Use the unit switch on the Term field to type the period in years, months, or days — or pick start and end dates from the calendar. Every option is converted to an exact year count (365.25 days per year) before the math runs, so all four give the same answer.

How is simple interest different from compound interest?

Simple interest is calculated only on the original principal, so it grows in a straight line. Compound interest is calculated on the principal plus any interest already earned, so it grows faster over time.

Can I use a fractional term?

Yes. You can enter decimals such as 2.5 years, and the interest scales proportionally with the time entered.

Primary sources

Sources and review notes

Methodology last checked Jul 14, 2026. Formula implementation is covered by deterministic unit tests. No financial professional review is claimed yet.