calendar-increment-monthcalendar-increment-month is a Lisp macro in `
calendar.el'. (calendar-increment-month MON YR N &optional NMONTHS) Increment the variables MON and YR by N months. Forward if N is positive or backward if N is negative. A negative YR is interpreted as BC; -1 being 1 BC, and so on. Optional NMONTHS is the number of months per year (default 12).