All i know is that i will never you forelife again and wont recomend it to anyone. My chart keeps changing my ovulation day from day 13 to 21 so i'm not sure whats going on but it would make sense for it to be on the 21st day as my cycles have been over 30 days lately and having ovulation day as the 13th would make a 28 day cycle.. OH WHY ARE OUR BODIES SO CONFUSING