Finance
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Simple Interest Calculator.
Calculate simple interest, future value, and investment growth over time
Set your values
Results update as you type.
Year-by-Year Growth Table
| Year / Period | Accumulated Interest | Ending Balance |
|---|---|---|
| Year 1 | $600.00 | $10,600.00 |
| Year 2 | $1,200.00 | $11,200.00 |
| Year 3 | $1,800.00 | $11,800.00 |
| Year 4 | $2,400.00 | $12,400.00 |
| Year 5 | $3,000.00 | $13,000.00 |
How to Use
Simple Interest Calculator estimates the flat rate return on an investment or loan. Unlike compound interest, simple interest is calculated only on the original principal.
This formula is commonly used for short-term loans, certificate of deposits, and flat-rate retail financial instruments.
FAQs
What is simple interest?
Simple interest is a quick method of calculating the interest charge on a loan or investment, calculated solely on the principal amount.
What is the simple interest formula?
The formula is Interest = Principal × Rate (%) × Time (in years). The total future value is the Principal plus the Interest.
How does simple interest differ from compound interest?
Simple interest is calculated only on the principal amount, while compound interest is calculated on the principal plus any accumulated interest from previous periods.
Cite this calculator
Canonical URL: https://mathify.one/en/finance/simple-interest
Cite as: Mathify. (2026). Simple Interest Calculator. https://mathify.one/en/finance/simple-interest
Use Cases
Estimate investment growth
Use this calculator to see how much a fixed deposit, bond, or other simple-interest investment will grow over a specified period. Enter your principal, rate, and time to get the future value.
Example: Invest $5,000 at 4% annual interest for 3 years to see the future value.
Calculate loan interest
Determine the total interest you'll pay on a simple-interest loan, such as a personal or car loan, by entering the loan amount, interest rate, and loan term.
Example: Borrow $10,000 at 6% for 5 years to find the total interest cost.
Frequently Asked Questions
- How do I calculate simple interest?
- Enter the principal amount, annual interest rate, and time period in years. The calculator uses the formula: Interest = Principal × Rate × Time. It then shows the interest earned and the total future value (principal plus interest).
- What is the future value in simple interest?
- Future value is the total amount you will have after the interest is added to the principal. It is calculated as Principal + (Principal × Rate × Time). This calculator displays both the interest and the future value for your investment or loan.
- Can I use this calculator for any time period?
- Yes, you can enter time in years, but you can also use fractional years (e.g., 0.5 for 6 months) or convert months to years by dividing by 12. The calculator assumes the rate is annual, so ensure your time is in years for accurate results.
Tips & Common Mistakes
Tips
- Ensure the interest rate is in decimal form if you're doing manual calculations, but the calculator accepts percentages directly.
- For time periods less than a year, convert months to years (e.g., 6 months = 0.5 years) to get accurate results.
- Double-check that the principal is the initial amount before any interest is added.
- Use the future value to compare different investment options or loan terms.
Common Mistakes to Avoid
- Using the interest rate as a whole number instead of a percentage (e.g., entering 5 instead of 5%). The calculator expects the rate as a percentage, so enter 5 for 5%.
- Forgetting to convert time to years when using months or days, leading to incorrect interest calculations.
- Confusing simple interest with compound interest; this calculator only computes simple interest, not interest on interest.
Last updated: August 13, 2026