$1,000 x 5% x 3 years
- Ending balance
- $1,150.00
- Principal
- $1,000.00
- Time
- 3 years
Simple Interest Calculator
Use this free simple interest calculator to calculate interest and ending balance from principal, annual interest rate, and time in years.
Formula steps Estimate limits shown Examples included Private history
Formula steps
- Convert 5% to decimal rate 0.05.
- Multiply principal by annual rate and time.
- Add simple interest to principal for the ending balance.
How to use the simple interest calculator
- Enter the requested dollar amounts, rates, terms, tax settings, or contribution details.
- Use rates as percentages, such as 6.5 for 6.5%, and check whether a field asks for a monthly or annual amount.
- Press the calculate button to see the answer, supporting metrics, and formula steps.
- Use the result as a planning estimate only, then copy it if the assumptions look right.
Common uses
Calculate simple interest for classwork or quick planning.
Compare simple interest with compound interest.
Estimate interest when interest does not earn interest.
Check a principal-rate-time formula quickly.
Examples
$150 interest, $1,150 ending balance
Simple interest estimate
No interest growth
Frequently asked questions
Plain-language answers about when to use the estimate, what your numbers mean, what is left out, and how privacy works.
When should I use the Simple Interest Calculator?
Use it for early planning and side-by-side comparisons, especially for tasks like these: Calculate simple interest for classwork or quick planning. Compare simple interest with compound interest. Treat the answer as a planning estimate, not a final quote.
What is the Simple Interest Calculator doing with my numbers?
In plain language: The calculator multiplies principal by annual rate and time, then adds the simple interest to principal for the ending balance. If the result seems too high or too low, first check whether each field expects a monthly amount, annual amount, dollar value, or percent.
What does this estimate leave out?
This does not include compounding, changing rates, payment schedules, fees, taxes, or account-specific rules. Real finance decisions can also depend on fees, timing, local rules, credit details, and provider-specific terms.
Does the site save my finance inputs?
No. The calculator runs in your browser tab. Recent answers stay only on the page while you use it, and they are not sent to a server.