As far as I know, the first day of your period is day 1 of the cycle which is a bit of a blow if your periods last for two weeks because you may find you only have two weeks before the next one starts. I used to hope that it would be two weeks for the end of the period but, sadly, it doesn't seem to work that way! I have found that the only way to combat long bleeds is to take more progesterone unfortunately.