How to Calculate the Number of Days Between Two Dates

Whether tracking the duration of an apartment rental lease, managing statutory contract response deadlines, or counting down the days until an international holiday, calculating the number of days between two dates is a frequent task.

Inclusive vs. Exclusive Counting

The most important decision when measuring days between dates is deciding whether your count is inclusive or exclusive.

• Exclusive Counting (Default Standard): Does not count the start date, or does not count the end date. For instance, the time between Monday morning and Tuesday morning is exactly 1 day (24 hours).
• Inclusive Counting: Counts both the starting calendar day and the finishing calendar day. In travel itineraries or hotel stays, if you arrive Monday and depart Tuesday, you have used facilities on 2 calendar days.

How Calendar Computations Work

To count days manually without a software tool:

1. Count the remaining days in the starting month after the start date.
2. Add the full day counts of all whole intervening calendar months.
3. Add the calendar day number of the target finishing date.
4. Check whether any intervening February contains a February 29 leap day!

Worked Example: Project Sprint Timeline

Calculate the days between March 12, 2026 and April 25, 2026 (exclusive):

• Days remaining in March: 31 - 12 = 19 days.
• Days elapsed in April: 25 days.
• Total days = 19 + 25 = 44 days.

If counted inclusively (including March 12), the total is 45 days.

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