从任何日期开始计算+N个月周期(考虑闰年)

I have a random starting date (e.g. 2012-09-19). I would like to be easily get the ending monthly cycles' dates after this date. However, the monthly cycles are not exactly 30 days, but they are from date to date, e.g. 19 September to 19 October.I have a random starting date (e.g. 2012-09-19)