Elapsed time and inclusive date counting
Elapsed time measures the number of midnight-to-midnight calendar days between the two selected dates, so the ending date is not counted as another full day. Inclusive counting adds one day and counts both selected calendar dates. This distinction is the common reason two otherwise correct date counts differ by one day.
How the calendar duration is formed
The years, months, and days result advances from the earlier date by whole calendar years, then whole calendar months, then remaining days. Month lengths and leap days are therefore respected instead of treating every month as a fixed number of days. Reversing the dates keeps the same magnitude and reports the direction separately.
Weekday count limitations
The optional weekday result removes the selected weekend pattern from the counted date range, then subtracts the number of weekday holidays you enter. It does not know a country, region, organization, court, or market holiday calendar. For legal, payroll, shipping, or regulated deadlines, confirm the exact inclusion rule, cutoff time, time zone, and holiday list with the governing source.