Ovulation & Due date confusion

[LStrawberry]

Hi, can anyone help me please! We’ve just started trying for baby number 3! My next ovulation date is the 5-11th of December with the 9th December circled as the actual ovulation date. So if by miracle I do fall pregnant next month when will the baby he due? I’ve counted 40 weeks from 9th on a calendar it takes me to the 15th September but on due date calculators online it’s coming up end of August 😅🤦🏼‍♀️ I’m really confused by it all and would love some insight. Obviously they go by your last period which for me would be November but I’m not pregnant now so I don’t understand how they add 2 weeks from your last period, should it not be calculated from day you actually conceive?

It’s 38 weeks from ovulation date / 40 weeks from first day of last period.

Unless it is IVF they use the date of your last period, so as PP said 40 weeks from last period.

Using last menstrual period (LMP) is the typical way to calculate pregnancy dues dates: 40 weeks from the day of you LMP.

The reason for this is that is impossible to say when you ovulate, conceive, implant, although there are usual patterns it is still not 100%. If you are tracking using BBT and have an established pattern this is easier.

Using the 40 weeks from LMP means that you are not technically pregnant for the first two weeks so this is the ('pre conception' phase)

So for example I ovulate day 17 of a 27 day cycle I'm 3 days 'off' a typical pregnancy. This would be adjusted at the dating scan at 12 weeks. But still my due date would be calculated using the 40 weeks from LMP.

I get your confusion, my SIL told me her theory. She believes it's because it's the 1st day of the egg's journey, I don't think it's true though.