Adding Days Across Month Boundaries
Adding days requires cascading through month capacities (31 days in January, 28/29 in February, etc.). Using pure epoch day arithmetic allows adding any integer value from 1 to 1,000,000 days instantaneously.
Month Addition and Month-End Pinning
What happens when adding 1 month to March 31? April only has 30 days. Standard calendar systems "pin" the date to the final available day of that month (April 30).
Common Practical Shortcuts
Common milestones include 30-day billing cycles, 60-day vendor payment terms, 90-day probationary windows, and 180-day passport validity requirements.