Simple Interest Calculator
Calculate simple interest and ending balance from principal, annual rate, and time.
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What this tool does
Calculate non-compounding interest with I = P × r × t, where the annual percentage rate is converted to a decimal and time is measured in years. The tool shows both interest earned or owed and the ending principal-plus-interest balance in your browser.
Simple Interest Calculator applies interest only to the original principal; previously earned interest never becomes part of the next period's interest base.
For example, 10,000 at 6% per year for 1.5 years produces 900 in interest and a 10,900 total because 10,000 × 0.06 × 1.5 = 900.
Use the result as a transparent baseline for a note, deposit, or classroom exercise, then compare it with the contract's actual day-count rule, fees, taxes, and compounding terms.
Where this tool earns its place
Reproduce the stated interest on a fixed-principal loan when the agreement uses a simple annual rate and a term expressed in years.
Create a non-compounding baseline before opening Compound Interest Calculator with the same principal, rate, and duration.
Check principal-rate-time exercises with a visible formula and a numeric result that is easy to recompute by hand.
What to check before relying on the result
- Performance and maximum practical input size depend on browser memory, device speed, and the structure of the input.
- Review the generated result before replacing or publishing an original file.
Open a nearby browser tool when you need to validate, convert, or reuse the result.
How to use
01Use Cases
Reproduce the stated interest on a fixed-principal loan when the agreement uses a simple annual rate and a term expressed in years.
Create a non-compounding baseline before opening Compound Interest Calculator with the same principal, rate, and duration.
Check principal-rate-time exercises with a visible formula and a numeric result that is easy to recompute by hand.
Tips & Tricks
- 01Normalize the time unit
The time input is years. Divide months by 12 before entering them; 3 months is 0.25 years and 18 months is 1.5 years.
- 02Enter a percentage, not a decimal rate
Type 6 for a six-percent annual rate. Entering 0.06 would mean 0.06%, one hundredth of the intended rate.
- 03Check the agreement's assumptions
This model keeps principal and rate constant and excludes compounding, payment timing, fees, taxes, and day-count conventions such as actual/360.
FAQ
02What formula does the calculator use?
It uses I = P × r × t. P is principal, r is the annual percentage rate divided by 100, and t is time in years. Total amount is P + I.
How would 10,000 at 6% for 18 months be calculated?
Convert 18 months to 1.5 years, then calculate 10,000 × 0.06 × 1.5 = 900 interest. The ending amount is 10,900.
Does simple interest compound?
No. Interest is calculated against the original principal for the entire term. Use Compound Interest Calculator when interest is periodically added to the balance.
Does the result include payments, fees, taxes, or day-count rules?
No. It is a principal-rate-time estimate. Real agreements may use scheduled payments, origination fees, taxes, or actual/360 and actual/365 conventions.
Can I use this result as financial advice?
No. The result is an informational estimate based on the values you enter. Check the math, fees, taxes, and local rules before making financial decisions.