We were trying for our second so I was tracking it. Luckily december was the least amount we had sex in the last few months so I didn't have to try very hard to figure out what day we conceived. It's not a big deal, but I feel kind of bad not going with what my doctor says: I said sept 21st and they did an ultrasound and I measured exactly 9 weeks with that due date but they are going by my period day which is the 22nd. It's really not a big deal but I still wanna go with the 21st.. Lol