Online Tool Store
Simple Interest Calculator
Calculate simple interest, final balance, annual earnings, and a clear year-by-year projection from principal, rate, and time.
🔒 This tool runs entirely in your browser. Your files are never uploaded to a server.
Estimate simple interest
Enter principal, annual rate, and time.
Example shown: $10,000 at 6.5% for 4 years.
Interest earned
Final balance
Interest per year
Calculation
26.0% growth$10,000 × 6.5% × 4 = $2,600
How it works
- Enter the starting principal amount.
- Add the annual interest rate and time in years.
- Review total interest, final balance, and annual interest instantly.
The simple interest formula
Simple interest uses I = P × r × t, where P is principal, r is the annual rate written as a decimal, and t is time in years. The final balance is P + I. For $10,000 at 6.5% for 4 years, interest is $10,000 × 0.065 × 4 = $2,600.
FAQ
What is the simple interest formula?
Simple interest equals principal multiplied by the annual interest rate as a decimal and the time in years: I = P × r × t.
How is simple interest different from compound interest?
Simple interest is calculated only on the original principal. Compound interest also earns interest on earlier interest, so its balance grows faster over time.
Can I enter part of a year?
Yes. Use a decimal such as 0.5 for six months or 1.25 for one year and three months.
Does this calculator provide financial advice?
No. It provides an educational estimate and does not include fees, taxes, changing rates, or lender-specific terms.
Are my figures uploaded?
No. All arithmetic runs locally in your browser.
How we compare
| Feature | Online Tool Store | Compound interest calculators | Spreadsheet formulas |
|---|---|---|---|
| Simple-interest result | Instant | Often secondary | Formula required |
| Formula explanation | Yes | Varies | No |
| Visual principal/interest split | Yes | Varies | Manual chart |
| Account required | No | Varies | No |
Choose this calculator for loans or investments that explicitly use simple interest and when you want the formula alongside the result.