Date Arithmetic & Working Day Calculations: Chronological Guide
Last updated: 2026-09-11 • Editorial Staff
Determining exact durations between dates or calculating business deadlines requires date arithmetic that accounts for month lengths, leap years, and weekend non-working days.
Project managers, HR professionals, and legal teams rely on working day calculations to schedule deliverables accurately.
Calendar Day Differences vs Business Days
Total Elapsed Days counts every consecutive 24-hour period between a starting date and ending date, including weekends and public holidays.
Business Working Days exclude non-working weekend days (Saturdays and Sundays) and optional corporate/national holiday lists.
Leap Year Rules in Date Algorithms
A year is a leap year if it is divisible by 4, except for century years (ending in 00) which must also be divisible by 400. Thus, 2000 was a leap year, but 1900 was not.
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