ADDMONTHS

AddMonths is a date-time operation found in many programming languages and libraries that adds a specified number of calendar months to a given date. The operation increases the month component by the provided amount and adjusts the year as needed, while typically preserving the day component when possible.

In typical implementations, if the original day of the month is not valid in the target month (for example, adding one month to January 31), the result is adjusted to the last valid day of the resulting month. Positive values add months, while negative values subtract months. Time-of-day components are usually preserved, though some libraries may apply normalization in tandem with calendar rules.

Common language examples include: in .NET, DateTime.AddMonths(int months) returns a new date with the specified months added; in Java, LocalDate.plusMonths(long monthsToAdd) or ZonedDateTime.plusMonths perform a similar operation; in JavaScript, libraries such as date-fns provide addMonths functionality. While behavior is broadly similar across platforms, exact edge-case handling can vary slightly, especially around end-of-month logic and time zone considerations.

Edge cases include arithmetic overflow (adding months that exceed the maximum date), crossing year boundaries, and interactions with time zones or daylight saving rules in certain data types. AddMonths is a core tool for generating recurring dates, payment schedules, or any feature requiring calendar-based date progression without manually incrementing month values.