This would go in the pregnancy forum or fertility.. But theres not really a way to know the exact day u concieve.. Unless uve only had sex that one time...But most doctors just calculate it from the 1st day of your last period. And then when u get an ultrasound later they can normal tell, give or take 2 or 3 days, around which day u conceived and will give u a new due date. Is there a reason u needed to know, or just curious?