i went through fertility treatmrnt a year ago. 14 days after the first day of your last period are the days you are fertile.
This is true for many women, but not all. Some will naturally ovulate sooner or later than the norm....and ocassionaly might even have a one off cycle where they ovulate outside of their own norm.
This is why women have to be careful if they are trying to become pregnant not to focus just on those days as they could miss their window even by a few days and that might make all the difference. ....important too if they are trying not to become pregnant and are using natural family planning. It is a good starting place.....about 12-16 days before your next period is due regardless of how long your cycle is, but watching for other signs that your body is preparing for ovulation can be helpful for each individual.