Simple Interest Calculator
Compute simple interest on a principal over time for loans or deposits.
How to use this tool
- Enter principal, annual interest rate.
- Set time (years, months, or days).
- Calculate interest and final amount.
How it works
Interest = principal × rate × time (in years). The tool converts months and days to years before applying the formula.
Tips
- Beware bundles with compounding clauses — use the compound calculator for those.
- Days-based quotes use 365 days; some lenders use 360.
Limitations
No interest on interest; for compound instruments use the compound calculator.
Frequently asked questions
What's the formula?
I = P × r × t, where P is principal, r the annual rate (decimal) and t time in years. Amount = P + I.
When is simple interest used?
Short-term loans, some bonds and promissory notes, where interest isn't added back into principal.
Can I enter days and months?
Yes — time can be given in years, months or days (days uses a 365-day year).