How to use it
1. Choose datesSelect a start and end date.
2. Choose the counting ruleInclude both endpoints for event or operating days.
3. Shift a dateEnter a positive or negative number of days.
DATE DIFFERENCE AND D-DAY
Calculate date differences
and calendar offsets.
Count days between two dates, include both endpoints when needed, or find a date a set number of days before or after another.
—
—D-Day notation—
Direction—
Including both dates counts the start and end date as full calendar days.
—
—Calendar differences use UTC day units to avoid daylight-saving transitions.
Examples
Project duration
July 1 to July 31 has a 30-day difference, or 31 days when both endpoints are counted.
Anniversary date
Add 100 days to a base date, then adjust separately if the first day must count as day one.
Find an earlier date
Enter -7 to calculate the date seven days before the base date.
Date-counting rules
The same two dates can produce different totals depending on whether endpoints are included.
Difference means elapsed days
The default difference from July 1 to July 2 is one day. It measures calendar dates, not elapsed hours.
Inclusive counting adds one
Use it when the first and last operating days both count. The same start and end date then equals one day.
UTC day units avoid clock shifts
Using fixed 24-hour UTC units prevents daylight-saving days of 23 or 25 hours from changing the calendar result.