ToolwebHow to use this tool
- Select a start date and an end date.
- Choose start-date inclusion and optionally set a day offset in More options.
- Read the interval and offset date separately, including the displayed weekdays.
Cross a leap-year February
- Input and settings
- 2024-02-28 to 2024-03-01; exclude start day
- Result
- 2 days; adding one day gives 2024-02-29
This is a calendar-date gap, not a count of elapsed clock hours.
What including the start day means
Two identical dates have a normal gap of zero days. Including the start counts that calendar date itself and gives one day. A reverse interval keeps a negative sign while start inclusion adds one to its magnitude.
The week value is the start-excluded calendar gap divided by seven. Its basis can differ from an inclusive count, so read the row label. Use Business days when weekends or supplied holidays need to be removed.
Calendar arithmetic without local-time drift
Inputs are parsed as year, month and day and converted to UTC day numbers. A two-date gap stays two calendar steps even where daylight saving makes a day 23 or 25 hours, and early years are validated without the legacy 1900-based constructor shortcut.
The supported range is years 0001–9999. Invalid dates such as February 30 and offsets that leave the range are rejected. Local legal-deadline rules, lunar calendars and holiday schedules are not inferred.
Common questions
Which time zone does the Today button use?
It selects the current local date on your device. Subsequent date arithmetic uses calendar day numbers independently of local clock times.
Can I add one month?
Offsets are integer days only. Because month lengths differ, the tool does not equate 30 days with one month.