Understanding Simple Interest
How we calculate. Simple interest = principal × annual rate × time in years. The form uses the same arithmetic as the worked examples on this page. See our methodology and accuracy policy.
Real-world scenario: A typical Simple Interest case uses principal 5000 and annual rate (%) 8. Enter the same figures below to reproduce the worked path.
What is Simple Interest?
Interest computed only on the original principal. It does not compound, so long tenures usually use compound or EMI formulas instead.
- Amount = P + Interest
- t can be fractional (e.g. 0.5 for 6 months)
- Not for most amortizing loans
The Formula
Worked Example
Common Use Cases
- Short-term lending: flat interest quotes
- Homework/finance class: SI problems
- Compare vs compound to show compounding impact
Pro Tips
- Convert months to years (months ÷ 12)
- Confirm if the quote is flat or reducing
- Taxes/fees are outside this formula
Limitations: Simple Interest results are educational finance aids—not loan offers, investment advice, or tax counsel. Confirm figures with a qualified professional and your contract.
FAQ
Simple vs compound?
Simple interest ignores interest-on-interest. Compound adds earned interest to the base each period.
Can t be months?
Convert to years first, or use t = months/12 in this calculator.
Authoritative References
For lending and investing concepts, consult:
- CFPB — consumer lending and mortgage education
- Investopedia — finance formula explainers
- SEC Investor.gov — investor education