How days between dates are counted
The calculator converts both dates to a day number on the calendar and subtracts. Because it works with real calendar dates, leap days and months of different lengths are counted exactly. It then expresses the same span in other ways: whole weeks, calendar years-months-days, and the number of weekdays that fall inside the period.
The method
days = end date − start date (+1 if the end date is included) weeks = days ÷ 7 (whole) and remainder days business days = full weeks × 5 + weekdays in the leftover days
The span is counted as the start date up to, but not including, the end date — the way “how many days until” is normally meant. Including the end date counts both ends.
Worked example
From March 15, 2026 to October 30, 2026:
Remaining days in March (17) + April 30 + May 31 + June 30 + July 31 + August 31 + September 30 + 29 days into October = 229 days, or 32 weeks and 5 days. On the calendar that's 7 months and 15 days.
Of those 229 days, 164 are Monday–Friday business days. Including October 30 itself would make it 230 days and 165 business days.
For a whole year, January 1 to December 31, 2026 is 364 days (365 with the end date), with 261 weekdays.
Limitations
- Public holidays aren't subtracted from business days.
- Times of day and time zones are ignored; every date is a whole calendar day.
- Uses the Gregorian calendar for all dates, including historical ones before its adoption.
Frequently asked questions
Does the count include the end date?
By default it doesn't: from Monday to Tuesday is 1 day. Tick "Include the end date" when both the first and last day should count — for example, a hotel stay billed by calendar day, or a leave request that runs Monday through Friday (5 days).
How are business days counted?
Business days are Monday through Friday within the period, using the same start and end rule as the day count. Public holidays are not removed, because they differ by employer and state; subtract them yourself if they apply.
How many days are in a year?
365 in a common year and 366 in a leap year. A year is a leap year if it is divisible by 4, except century years, which must be divisible by 400 — so 2000 was a leap year and 2100 won't be. The calculator follows these rules automatically.
What if the end date is before the start date?
The calculator still works and tells you the second date is earlier. The number of days is the same either way.
Why does the months answer look uneven?
Months are counted on the calendar. From January 31 to February 28 is less than one whole month, while from February 28 to March 28 is exactly one, even though it is only 28 days.