Find simple interest or solve principal, annual rate and duration. Compare scenarios, choose Actual/365, Actual/360 or European 30E/360, and review an optional non-compounding schedule.
01 / CALCULATION MODE
Simple interest = principal × annual rate × year fraction. Interest is calculated on original principal only.
02 / ENTER YOUR DETAILS
Enter both dates to override numeric duration. Actual counts use UTC calendar days (including leap days). 30E/360 uses 30-day months and a 360-day year. Without dates, months use 12 equal months and days use the chosen year denominator.
Enter a principal, rate and duration or dates to calculate interest.
04 / COMPARE SCENARIOS
Results are mathematical estimates using the selected day-count convention and currency rounding, not financial advice. Your inputs stay in your browser.
Choose an interest or reverse-solving mode.
Enter duration or both dates and select a day-count convention.
Review simple interest and maturity, compare scenarios and export the schedule.
Choose a calculation mode, enter principal, annual rate and days, months or years, or provide both start and end dates. Pick a day-count convention, compare an independent scenario, then copy or download the results.
Handles leap-year calendar dates, reverse calculations, currency-aware rounding and an annual non-compounding schedule with cumulative interest. No uploads or accounts.
Your inputs are calculated in your browser only. Interest and maturity figures are mathematical estimates, not financial advice.
Simple interest equals principal multiplied by annual rate and the selected fraction of a year. Interest is never added to principal for the next period.
Both count actual elapsed UTC calendar days, including leap days. Actual/365 divides those days by 365; Actual/360 divides by 360.
It treats every month as 30 days and a year as 360 days, using day 30 for the 31st in start and end dates. This is a mathematical convention, not the same as actual calendar days.
Yes, enter known interest and the other inputs. Zero principal, zero rate or zero duration can make a reverse calculation undefined; the calculator reports an error instead of dividing by zero.
No. Period interest comes from the original principal and the elapsed year fraction. Cumulative rounding is reconciled to the displayed total without earning interest on prior interest.
A numeric year is one year and a numeric month is one-twelfth of a year. Days use the chosen 365- or 360-day denominator. Enter both dates to use actual calendar days.