your cyle is taken from the day your period starts, thats day one, so when tracking ovulation depending on how long your cycle is its usually around day 14 for a 28 day cycle, but this can vary from women to women. In pregnancy they also clculate your cycle/bubs age from the first day of your last menstral cycle, this can confuse alot of people as you are told you are 8wks pregnant when bub is only 6wk, this is just they way they do it. Hope this helps you somewhat