If I started my cycle on September 17 2012 when do I supposed to start in October

Hi TinSin, If your period is pretty regular (on time every month) then your cycle for October would be due on the 15th. It should be every 28 days, so you count 28 days from the day it started the month before. Not every woman is regular until they get a little older, and your cycle can be thrown off by numerous things, such as diet, and emotional stress. I hope this helped. Good luck.