I am a little confused about calculating due dates for pregnancy. As far as I know, doctors always count 40 weeks from the first day of your last period, but the actual pregnancy lasts 38 weeks from conception/ovulation. I have longer cycles and usually ovulate around day 24, not the average day 14. Does this mean my due date will be out by about 10 days? How does this work? I know doctors do it from first day of last period for consistency but unsure how it works when you know you definately ovulated around day 24. Anyone else had a similar situation?