Why is “same day next month” not always a simple calculation?

Answer: Because months have different lengths, so some dates do not map neatly

Because months have different lengths, so some dates do not map neatly ✓ — Correct! Calendar arithmetic is tricky because months vary in length, so dates like January 31 do not fit neatly into every following month.

Because computers stop counting after 30 days — Wrong. Computers do not stop counting after 30 days.

Because time APIs only support weeks, not months — Wrong. Time APIs do support months; the challenge is that month arithmetic follows calendar rules, not fixed durations.