Calculate simple interest
- Enter principal and an annual interest rate.
- Choose duration and its unit. Check your agreement’s day-count convention.
- Calculate and copy or download the result.
Formula and example
Interest = principal × annual rate ÷ 100 × years. Total = principal + interest. Months convert to years by dividing by 12; days divide by 365. The principal stays fixed and interest does not earn further interest.
For 1,000 units at 10% per year for 2 years, interest is 200 and total is 1,200. For 6 months, interest is 50. The HDFC Mutual Fund simple-interest reference describes the principal, annual rate and time formula.
Assumptions and limits
This is a constant-principal calculation, not a reducing-balance EMI schedule. It excludes repayments, compounding, fees, taxes and rate changes. A day is 1/365 year even in a leap year; Actual/Actual or 360-day agreements can produce different results. The tool does not infer calendar dates. Duration can be fractional and must be equivalent to 0–50 years: 0–600 months or 0–18,250 days. Principal: 0.01–1 trillion units; annual rate: 0–100%.
Results are estimates, not advice or a lender quote. Display follows currency precision, with scientific notation for tiny nonzero values. CSV exports six decimals, preserving tiny nonzero amounts in scientific notation. All inputs remain in browser memory with no upload or saved financial values. Reset clears output and restores defaults. Worked examples load a draft in your selected currency. Undo recovers raw inputs, duration unit, currency search and the accepted result after Reset or either example, including after recalculation. Editing discards the recovery snapshot.
Does this calculate a monthly loan instalment?
No. It computes interest on a constant principal. Use the EMI calculator for a fixed-rate loan paid down monthly.
Why choose days rather than months?
Use days when your duration is specified in days and the agreement uses a fixed 365-day year. A calendar month does not always have the same number of days.