When to use this calculator
Estimate interest when it is calculated only on the original principal. Shows interest only; add principal to get the ending balance. Excludes fees and tax.
Explore the savings & interest calculators for other questions in this topic. For a related calculation, use the Amortization Schedule Calculator: Calculate a level monthly payment and a month-by-month principal-and-interest schedule.
PUTTING IT INTO PRACTICE
Simple Interest: a worked example
The values below are an illustrative example, not a recommendation. Replace them with measurements or assumptions that match your question.
| Input | Example value |
|---|---|
| Principal | 1,000 |
| Annual interest rate (%) | 5 |
| Years | 3 |
| Result | 150 currency units |
- Check the input labels and enter the example values above.
- Apply the relationship: Interest = principal × annual rate ÷ 100 × years.
- The result is 150 currency units, rounded for display.
How to interpret your result
Shows interest only; add principal to get the ending balance. Excludes fees and tax.
Match the quoted rate to its compounding convention. A nominal rate, effective annual rate and continuous rate are not interchangeable. Contribution timing also matters when interest is included in a future-value model.
Frequently asked questions
Is a future savings value a forecast?
It is a scenario based on your entered rate and contributions. Changing rates, fees, tax or interrupted payments can change the actual outcome.
How do I use the simple interest calculator?
Enter principal, annual interest rate (%), years. The result updates automatically. Use the units shown beside each input; the example values illustrate the method.
Which formula does this calculator use?
Interest = principal × annual rate ÷ 100 × years.
What should I check before using the result?
Shows interest only; add principal to get the ending balance. Excludes fees and tax.
How are results rounded?
Scalar numbers display up to six decimal places, with scientific notation for very large or small values. Text, fraction, date and schedule outputs use the format described on the tool. Intermediate calculations use JavaScript floating-point arithmetic. Keep sensible precision for your measurements.
Further reading
For background on this topic, see OpenStax: compound interest ↗. This is a topic reference, not an external review or endorsement of this tool.
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