Everyone says pregnancy lasts nine months but it's not that simple - here's how to work it out
There are some things you can be certain of, how long pregnancy lasts being one.
But while we all have gone throughout our lives thinking we add nine months to work out when a baby is due, it's not exactly right.
It takes about 38 weeks from the day you conceive to the day you deliver, which isn't nine months.
Very few mums-to-be know exactly when they conceived, but if you've had sex just once during your fertile period you may not have actually conceived then. In fact the sperm may have just hung out in the fallopian tube for a few days until a egg came its way - the fertilised, then the baby is conceived.
If that sounds a bit too complicated, there is a way of working out the due date.
There's a simple equation you can do before your ultrasound that can tell you when your baby is likely to be due
While most people just estimate, most doctors will simply count from the first day of your last period. If you have a regular period, at an average length, that day is usually about two weeks before conception, which is why pregnancies are said to last 40 weeks - nearer 10 months than the nine we usually refer to.
So doctors will add 280 days from conception (40 weeks).
There's the added warning that this method doesn't take into account how long your menstrual cycle is.
How to work our a due date for yourself
First, remember only 1 in 20 women delivers on her due date so this is just a rough guide.
If you don't know when you conceived
Take the date of your first day of your last period.
Add 40 weeks.
If you do know when you conceived
Just add 38 weeks from your conception date.
Quick way to work out by month
You can roughly work out when baby will be here by month - and it's fairly simple
This is a really rough guide, so bear this in mind when using it.
January - October
February - November
March - December
April - January
May - February
June - March
July - April
August - May
September - June
October - July
November - August
December - September