How to Calculate the Days Between Two Dates
Elapsed days, inclusive counting, month and year boundaries, leap February, and full weeks.
Calendar Guides
Five complete articles tied to the calculators on this site.
How to Add or Subtract Days From a Date
Calendar-day arithmetic, weekends included, with a negative-adjustment example.
Business Days vs Calendar Days: What's the Difference?
Weekdays, weekends, endpoints, and why public holidays stay in this calculator.
How to Find the Day of the Week for Any Date
The seven-day week inside the supported Gregorian range, without DST distortion.
How Date Calculators Handle Months, Years, and Leap Days
Clamp-to-last-valid-day, February 29, and why years are applied before months.