Finance

Free Simple Interest Calculator Online

Use this free simple interest calculator to quickly find the interest earned or owed on a principal amount over a fixed period. It works as a straightforward interest rate calculator for loans, deposits, and savings where interest does not compound - just enter the principal, rate, and time to get an instant result.

Principal amount

Annual interest rate

Time period

Interest earned

Principal$0

Total amount$0

Simple interest grows at a fixed pace. If your rate compounds instead, try the Compound Interest Calculator to see how much more you could earn over the same period.

What is simple interest and why it matters

Simple interest is interest calculated only on the original principal amount, for the entire length of the loan or deposit - it never earns interest on interest already accrued, unlike compound interest. This makes it predictable and easy to calculate by hand, which is exactly why it is still used for many personal loans, car loans, short-term deposits, and some bonds. Knowing how simple interest works matters whether you are comparing loan offers, estimating how much a fixed deposit will earn, or just trying to understand a bank statement - because a loan advertised with a "simple interest rate" will cost less over time than the same rate compounded, and the difference grows the longer the term runs. Understanding this distinction before signing a loan agreement or opening a deposit account can meaningfully change which offer is actually the better deal.

How this calculator works

This tool uses the standard simple interest formula, I = P x r x t, where P is the principal amount, r is the annual interest rate as a decimal, and t is the time period in years. If you enter the time period in months or days instead, the calculator automatically converts it to years first (dividing months by 12, or days by 365) before applying the formula, so the result stays accurate regardless of which unit you choose. The total amount shown is simply the principal plus the interest earned. Nothing you type is sent anywhere - the calculation happens instantly in your browser.

Common searches this calculator answers

How much interest will I earn on a fixed deposit or savings account?
What is the simple interest formula and how do I use it?
How much will a personal or car loan cost in interest?
What is the difference between simple interest and compound interest?
How do I calculate interest for a period in months or days?
How much total will I owe on a simple interest loan?

How to use it

Enter the principal amount - the original sum being loaned, deposited, or invested.
Enter the annual interest rate as a percentage.
Enter the time period, and choose whether it is in years, months, or days.
Read the interest earned, along with the total amount (principal plus interest).
Compare the result against the Compound Interest Calculator if your actual rate compounds instead of staying simple.

Tips

Always check whether a loan or deposit is advertised as "simple" or "compound" interest - the wording changes the real cost or return significantly over longer terms.
For short-term loans (under a year), simple interest and compound interest produce very similar results, so the distinction matters most for longer periods.
When comparing two loan offers, convert both to the same time unit before comparing rates, since a monthly rate and an annual rate are not directly comparable.
Use the days option for very short-term lending or late payment interest calculations, where months or years would be too imprecise.
Re-run the calculator with a slightly higher rate to see a conservative worst-case estimate alongside your expected one.

Frequently asked questions

Is this simple interest calculator free to use?

Yes. It is free, runs entirely in your browser, and does not require an account or sign-up.

What is the difference between simple interest and compound interest?

Simple interest is calculated only on the original principal for the entire term. Compound interest is calculated on the principal plus any interest already earned, so it grows faster the longer the term runs. Use the linked Compound Interest Calculator to compare the two directly.

Can I calculate interest for a period in months or days instead of years?

Yes. Choose months or days from the time period dropdown and the calculator will convert it to the correct fraction of a year automatically before calculating.

What types of loans or deposits use simple interest?

Simple interest is common for many personal loans, auto loans, short-term promissory notes, and some certificates of deposit. Savings accounts and credit cards, by contrast, typically use compound interest.

Is the result from this calculator guaranteed to match my bank or lender?

This tool provides a standard simple interest estimate based on the numbers you enter. Actual loan or deposit terms can include fees, different day-count conventions, or other adjustments, so always confirm the exact terms with your bank or lender.

Why is my interest amount lower than I expected?

If you expected compound growth, simple interest will always produce a lower total over the same rate and term, since it does not earn interest on previously accrued interest. Try the Compound Interest Calculator to see the compounded version of the same numbers.

Does this calculator account for taxes or fees?

No, the result shown is the interest and total amount before any taxes, fees, or penalties that may apply to a real loan or deposit.

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