So, I'm 31 weeks with DC2 and I STILL don't know how to make 9 months from 40 weeks...

[norktasticninja]

I get a lot of looks when people ask how many months I am and I don't know, how on earth does the whole 9 months from 40 weeks thing work? Please enlighten me

You can't. Because its actually 10 months. More or less.

It doesn't really work because a month does not equal 4 weeks all the time.

And you're about 7 months at 31 weeks.

It's not 10 months!

If you want to know how many months you are then just count actual months based on calendar date of lmp.

I always thought that you acually have to finish the final 9th month too..so it is actually more like 10mths no? Thats how a midwife described it to me many years ago.

There are 365 days and 12 calendar months in a year - so an "average" calendar month is 365/12 = 30.42 days. So if an average pregnancy lasts 40 weeks, that's 40*7 = 280 days, which is 280/30.42 = 9.2 "average" months.

A lunar month (that is the time taken for one complete cycle of the moon) is 28 days, and there are 13 lunar months in a year or 10 lunar months in an average pregnancy.

just take your due date - assume approx 11th June - and work back.

So today you have 2m to go. You must be 7m

Don't forget the 40 weeks actually includes 2 weeks when you're not pregnant.

I'm in France and the way they do it here is they count 9 months from estimated date of conception, which gives something like 41 and a half weeks to due date.

So to know how many months you are, you just count calendar months from your date of conception, which is at the end of your second week from lmp.

You ignore the weeks completely.

Does that make sense?

Pregnancy is 9 calendar months and 1 week from your lmp date (based on 28 day cycle). I don't work in months either. Never have and I'm on my 5th.

I counted alternate 4 weeks and 5 weeks - so
1 month = 4 weeks
2 months = 9 weeks
3 months = 13 weeks
4 months = 18 weeks
5 months = 22 weeks
6 months = 27 weeks
7 months = 31 weeks
8 months = 35 weeks
9 months = 40 weeks

which is a bit of a faff
and both my pregnancies were 42 weeks plus anyway... but it does compensate for the fact that a calendar month is not 4 weeks long.
(Disclaimer: Olissa's arithmetic may be off due to wine!)