Date calculator

We use the Gregorian calendar without times or timezones. Differences exclude the chronologically earlier date and include the later date; including both adds the earlier date. Reversing the dates changes the sign. Addition/subtraction excludes the starting date; zero keeps the original date.

Years 0001–9999; up to ±1,000,000 days when adding or subtracting. Business days exclude only Saturday and Sunday: no public holidays or company calendars. Use a negative number to subtract days.