Simple Interest Calculator
Free online simple interest calculator. Enter principal, annual rate, and years to get interest earned and total amount with the simple interest formula.
Guide
What is simple interest?
Simple interest is calculated only on the original principal for the full term. Interest does not compound onto the balance, so each year earns the same dollar amount of interest when the rate and principal stay constant. Use this online calculator when you need a fast financial estimate for loans, notes, or savings that quote a simple interest rate rather than a compounding schedule.
Simple interest formula
Interest = Principal × (Annual rate ÷ 100) × Years. Total amount = Principal + Interest. The principal must be greater than zero, the annual rate must be zero or greater, and the term in years must be greater than zero.
Worked example
A 10,000 principal at 5% simple interest for 10 years earns 10,000 × 0.05 × 10 = 500 in interest each year, for 5,000 total interest. The total amount is 15,000. Enter the same values above to reproduce the result and share the calculation URL.
Assumptions and limitations
This Calculator assumes a fixed principal, a constant annual rate, and a continuous term measured in years. It does not model compounding, fees, taxes, partial-year day-count conventions, or changing rates within the term.
Common questions
Answers to the most common questions about calculating simple interest online with this formula-based financial calculator.
How do I calculate simple interest?
Multiply principal by the annual rate as a decimal and by the term in years. Interest = Principal × (Annual rate ÷ 100) × Years. Add that interest to the principal to get the total amount.
What is the simple interest formula?
Interest = Principal × Rate × Time, where Rate is the annual percent divided by 100 and Time is years. Total amount = Principal + Interest.
How is simple interest different from compound interest?
Simple interest applies only to the original principal for the full term. Compound interest applies to the growing balance, so interest earns interest over time.
Can I use fractional years in this calculator?
Yes. A term such as 2.5 years is valid. The Calculator scales interest linearly with the entered term.
Does a zero rate return only the principal?
Yes. Total interest is zero and the total amount equals the principal.
Is this a free online simple interest calculator?
Yes. It runs in the browser with no sign-up. Results are educational estimates, not financial advice.
Methodology
The Calculator uses exact decimal arithmetic for validation and calculation, then rounds values only for display. Total amount is computed as principal plus interest at internal precision.