This free date calculator computes the difference between two dates and allows adding or subtracting calendar days or business days with full holiday support.
The Gregorian calendar is the most widely used civil calendar in the world today. Introduced in October 1582 by Pope Gregory XIII, it reformed the Julian calendar to more closely align with the Earth's solar orbit of approximately 365.2422 days.
To maintain astronomical alignment, the Gregorian calendar uses the following leap year rules:
Standard business weeks consist of 5 days: Monday, Tuesday, Wednesday, Thursday, and Friday. Saturdays and Sundays are classified as weekends.
In federal and commercial practice, if a holiday falls on a Sunday, it is observed on the following Monday. If it falls on a Saturday, it is observed on the preceding Friday.
Standard date subtraction calculates the difference between dates (e.g. from Monday to Tuesday is 1 day). Enabling "include end day" counts both the start date and the end date as full active days (e.g. Monday and Tuesday count as 2 days).
If you add 1 month to January 31, the target month (February) has only 28 days (or 29 in a leap year). The calculation caps the result to the last valid day of February (February 28 or 29).
This calculator uses astronomical year numbering for CE dates. For historical dates before 1582, the Gregorian calendar is applied proleptically.