Adding months to dates in JavaScript requires careful handling of varying month lengths and edge cases. The native `setMonth` method can cause overflow issues when adding months to dates like January 31st. Custom functions can enforce end-of-month semantics for billing scenarios by checking if the day overflowed and adjusting to the last day of the target month. The `date-fns` library provides `addMonths` and `subMonths` functions that handle edge cases cleanly. For timezone-aware applications, combining `date-fns` with `date-fns-tz` prevents DST-related formatting issues. The choice of approach depends on the use case: custom end-of-month logic for billing, `date-fns` for UI calendars, and native methods for internal UTC timestamps.
