dayOfMonth

DayOfMonth refers to the day component of a calendar date, indicating the day within the current month. For example, the date 2025-04-23 has a dayOfMonth of 23. The term is used across many date and time representations to separate the month and year from the day.

The typical range for dayOfMonth is 1 through 31. Each month has a different maximum day, with February having 28 days in common years and 29 days in leap years. Any day value outside the valid range for a given month is considered invalid in strict date representations and may trigger validation errors or automatic adjustment by date libraries.

In software development, dayOfMonth is a standard field in date/time types. It is often exposed as a property named day, dayOfMonth, or dayOfMonth depending on the language or library. Examples include Java's LocalDate.getDayOfMonth(), Python's datetime.day, and JavaScript's Date.getDate(). SQL databases provide similar access through functions like extracting the day from a date.

Operations involving dayOfMonth interact with month length. Adding or subtracting days can roll the date into adjacent months or years, and changing the month may require clamping or adjusting the day if the current day exceeds the target month's maximum. Some date libraries offer safe constructors or normalization routines to prevent invalid dates.

See also: day of week, day of year, calendar arithmetic, ISO date.