Due date calculating

[TTCnewbies]

Doesn't apply to me as not tested this month yet but out of interest, will due date always go from first day of last period?

Yeah first day of last period.

Yeah that's right.

Not quite. Unless you mean, is that how the midwife calculated it initially?

Due date is 38 weeks from conception. The average conception takes place 14 days after the last period so that's why they date from last period initially and then adjust once you're scanned.

Two women could have a period on the same day and one ovulate on day 10, the other on day 24. They would be due 2 weeks apart, but would have had the same period date iyswim.

Some online due date calculators let you enter conception date if you know it. I ovulate nowhere near day 14 so I just adjusted accordingly.

That's how they initially calculate it but it will be refined at your 12 week scan. Mine changed by 6 days.

Day one of last period is day 1 of 40 weeks of pregnancy. This gives an initial due date. The 12 week scan then gives a more accurate one, and the date which medical staff will use for the foreseeable.

Thanks all. It's hypothetical at the moment but it's to do with a holiday we are going on and if I was pregnant, the first day of last period would mean we can't go, but if it was adjusted by a week or 2 then we could. So was wondering exactly how it's calculated.

Would the date differences put you past the fit to fly time of pregnancy?

Your absolute due date is confirmed at 12 week scan. Regardless of whether or not you think this is correct based on ovulation dates etc this is what will be on all your medical records. Prior to this your due date is estimated at 40 weeks after the first day of your last period.

Yes! From first day of last period = no holiday. By about 1.5 weeks.
It doesn't matter, just one of those things. But got me curious. And all hypothetical as I feel like AF is on its way!

According to my mum who’s well into her 70s now and worked in a maternity unit baby’s due date was always calculated as being 9 months from the first day of your period plus another 7 days.