About the Date Difference
The calendar result expresses the gap as years, months and days, the way people say it: 2024-01-31 to 2024-03-01 is 1 month and 1 day, because adding one month to 31 January lands on 29 February (the last day of that month) and one more day reaches 1 March. The total-days figure is exact and independent of month lengths, and it is converted to weeks, hours, minutes and seconds. The “Include end date” option adds one day, which is what you want when counting inclusive ranges such as a hotel stay or a leave request.
Business days count Monday to Friday between the start date and the end date, excluding the end date unless you include it. Public holidays differ by country, region and year, so they are not subtracted — deduct them yourself if you need a payroll-grade number. All calculations treat the times you enter as wall-clock values, so a daylight-saving change inside the range does not turn a day into 23 or 25 hours.
The second panel adds or subtracts a duration. Years and months are applied first with end-of-month clamping (31 January + 1 month = 28 or 29 February, the same rule used by Java's LocalDate.plusMonths, .NET's DateTime.AddMonths and date-fns), then weeks, days, hours and minutes. The result shows the weekday, the day of the year and the ISO 8601 week number (weeks start on Monday; week 1 contains the first Thursday of the year).
How to use it
- Enter a start and an end date (and optionally a time).
- Tick “Include end date” if both the first and the last day should count.
- Read the calendar difference, total days, business days and the other units.
- To shift a date, enter it in the second panel, choose Add or Subtract and fill in the amounts.