How do I calculate my due date? Every website seems to give different answers!

[TalkingBack]

I know the first date of my last period was 25/1/10 and that my cycle is 39 days but I can't work out how many weeks I am.

Is there a reliable way of knowing?

30 days not 39!

Do you know when you ovulate? Pregnancy is supposed to be 38 weeks from the ovulation when you conceived - using the assumption that women ovulate on day 14 of a 28 day cycle that gives you 40 weeks from the 1st day of your last period.

If you don't know when you ovulated then, for simplicity, its probably easiest to calculate your due date as 40 weeks after the 25/1/10 + 2 days (for the 28+2 day cycle) - which I think is the 1st November.

(meant to add - if you know that you ovulated other than on day 16 of your cycle then you might want to tweak the EDD. However, the NHS don't seem to be very good at accepting that some women are very aware of what their bodies are doing and take a lot of persuading that the woman might have information worth considering - unless its something you feel very strongly about and/or it would shift your EDD by nearly a week then you might decide its an argument not worth fighting at this point. Could be worth bearing in mind if you go beyond 40 weeks past LMP and don't want to be induced, though).

Oh - and congrats on your pregnancy

Thanks Tangle, I know I would have concieved between the 7th and 10th Feb. My husband was away a lot of last month so I can quite accuratly pinpoint the dates. I have my booking in appointment next week, is it worth telling the midwife this do you think?

Yep, just tell the midwife you have long cycles.

It isn't an exact science anyway, I think anywhere between 37 and 42 weeks is pretty normal.

They might refer you for a dating scan if you can't settle on one. Alternatively pick a date you like which is around about the right time and go with that (even if only in your head).

Possibly getting into TMI, but when you had sex isn't a very good indicator of when you conceived - the perceived wisdom is that sperm can survive for upto 5 days. It gives you an earliest possible conception date, but the latest is still open ended. Ovulation is considered a better guide as the egg needs to be fertilised within 24 hours of being released.

Some women find it less agro to work out what they believe to be their EDD and then back calculate when their LMP would have been if everything was "average" - and then give the tweaked LMP date to the MW. Just be prepared that however precise you think you've been, the scan may show something different (although by 13 weeks there's about a weeks error on those measurements anyway), and any EDD is an estimate.

40 weeks from the first day of your last period.

Once you've calculated your due date, write it on a piece of paper and throw it away. Every health professional you meet will use a different due date, the scans will give different dates and the baby will fail to arrive on any of them.

I knew exactly when I concieved as baby was IVF so I knew exactly when they had removed and fertilised the eggs. This was not good enough for my GP, MW, consultant etc. who all chose to use a different date one week earlier. I was panicking as I was induced 2 weeks before my due date with DC1, and didn't want them trying to induce me 3 weeks before real due date with DC2.

Your due date will be 1st November.Add a week to your LMP then deduct 3 months. The midwife/hospital will base it on a 28 day cycle whatever you say is normal for you.
Congratulations!

What is LMP?