i NFP so i generally try to count from the conception date; the problem with this is, none of the calculators use this. so, though i pinpoint my due date from conception date, i follow the calendar for my last menstral. thankfully this time around, i actually somehow have managed to have about a 28 day cycle (before my ds i could go from 30 to 45...), so the dates are only a day or so apart. if i go from conception (which actually was several days after actual intercourse--must have had some really good mucus this cycle...) my idea of first trimester doesn't fit with theirs. hard to think of yourself as 2 weeks along when you weren't even pregnant, you know?