EDD?!?! Do you go by your LMP or conception date? I'm not exactly sure of my exact conception date…

EDD?!?!

Do you go by your LMP or conception date? I'm not exactly sure of my exact conception date but I didn't get a positive OPK until cycle day 23. I feel like if I go off my LMP, my due date will be way off and baby will be measuring way behind. Wondering what you girls use? Especially those that ovulate later than the "usual cycle day 14."