gen-define-the-duration-arithmetic-across-months-and-give-one-sh-b85e

Define the duration arithmetic across months and give one short worked example.

# Duration Arithmetic Across Months ## Definition Duration arithmetic across months involves adding or subtracting a number of months to/from a date. The key rule is: **When adding/subtracting months, preserve the day-of-month where possible. If the target month has fewer days than the original date's day, use the last valid day of the target month.** ## Rules - Add/subtract months to the month component - Keep the same day-of-month if it exists in the target month - If the day doesn't exist (e.g., Jan 31 + 1 month), clamp to the month's last day ## Worked Example **Problem:** What is 3 months after January 31, 2024? **Solution:** - Start: January 31, 2024 - Add 3 months: January → February → March → April - Target month: April 2024 - Try to preserve day 31: April only has 30 days - **Result: April 30, 2024** --- **Another case:** January 15, 2024 + 3 months - April has day 15 ✓ - **Result: April 15, 2024** (day preserved)