BYMONTH

BYMONTH is a component of the iCalendar recurrence rule syntax (RRULE) used to define repeating events. It specifies the months of the year during which occurrences may take place and serves to refine when an event can occur within its repeating cycle by restricting the months in which an instance is generated.

Values for BYMONTH are integers from 1 to 12, corresponding to January through December. Multiple months can be listed, and the rule will apply to each specified month within the recurring pattern.

BYMONTH is typically used in combination with the FREQ parameter, most commonly FREQ=YEARLY, to select particular months in each year. For example, RRULE:FREQ=YEARLY;BYMONTH=12 would produce occurrences in December of each year. It can also be combined with other BY* components, such as BYMONTHDAY or BYDAY, to further specify the exact days within the chosen months.

Support and interpretation may vary by calendar software. Most modern applications that implement the iCalendar format recognize BYMONTH, but some programs may ignore complex combinations or fail to expand certain rules. As with other RRULE parts, BYMONTH is a formal specification intended to guide software in expanding repeating events.

See also RRULE, BYMONTHDAY, BYDAY, FREQ, DTSTART, iCalendar, RFC 5545.