// enter principal, rate, and time to get interest earned
Calculate simple interest instantly. Enter principal, annual rate, and time to get total interest earned, final amount, and a year-by-year breakdown.
Ready to calculate
Enter principal, rate, and time then click CalculateType the initial amount (principal) you're investing or borrowing.
Enter the annual interest rate (%) and the duration in years or months.
Click Calculate to see total interest, final amount, and a period breakdown.
Simple Interest is calculated on the original principal only, unlike compound interest. The formula is: SI = P × R × T ÷ 100, where P = Principal, R = Rate per year, and T = Time in years. The total amount returned is A = P + SI.
Simple Interest = (Principal × Rate × Time) ÷ 100, or SI = PRT/100. The total amount is A = P + SI. Unlike compound interest, SI is always calculated on the original principal.
Simple interest is calculated only on the original principal. Compound interest is calculated on the principal plus accumulated interest, causing the balance to grow faster over time.
Yes! Use the dropdown next to the Time field to switch between Years and Months. The calculator automatically converts months to a fractional year value for the formula.
The table shows the cumulative interest earned and total account balance at the end of each period (year or month), up to a maximum of 50 rows for readability.
This tool uses the standard SI formula and is accurate for simple interest products. Real-world loans may use compound interest or different compounding frequencies — always check with your lender.
The calculator supports principals up to 1 trillion ($1,000,000,000,000). Rates are capped at 1000% and time at 1000 units to keep results meaningful.
A Simple Interest Calculator is an online tool that quickly computes the interest earned or owed on a principal amount over a given period, using a fixed annual rate. Whether you're a student solving a math problem, a saver estimating returns, or a borrower checking loan costs, a simple interest calculator gives you an instant, accurate answer without manual arithmetic.
Unlike compound interest — where interest is added back to the principal and generates further interest — simple interest is always calculated on the original principal. This makes it predictable, transparent, and easy to verify by hand.
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The universally accepted formula for simple interest is:
SI = (P × R × T) ÷ 100
Where:
The total amount at the end of the period is: A = P + SI.
For example, if you invest $5,000 at 6% per year for 3 years, the simple interest is $5,000 × 6 × 3 ÷ 100 = $900, and the total amount is $5,900.
Using this tool takes just a few seconds:
You can copy the breakdown table to your clipboard for use in reports, spreadsheets, or study notes.
It's important to understand the difference between simple and compound interest:
For long-term savings, compound interest can produce significantly more returns. For short-term borrowing or straightforward calculations, simple interest is easier to understand and budget for.
Simple interest appears in many everyday financial situations:
When the time period is given in months rather than years, simply select "Months" in the dropdown. The calculator divides the number of months by 12 to convert to years before applying the formula. For example, 18 months = 1.5 years. So SI at 8% on $2,000 for 18 months = $2,000 × 8 × 1.5 ÷ 100 = $240.
While the formula is straightforward, an online calculator saves time, reduces errors, and provides additional value through its breakdown table. Instead of recalculating for each year or month manually, you get an instant tabular view of how your balance grows over the entire term. This is especially useful when comparing multiple scenarios — change the rate or time and recalculate in seconds.
This tool is entirely browser-based: no data is sent to any server (except for the lightweight API call for calculation), no account is needed, and results are available instantly on any device.