Where is this two weeks added from??

[UpTheBumNoBabies]

So, I know the exact date I conceived, which was the 16th April.
But all the due date calculators use your lmp to give you your edd so they're saying I'm over 5 weeks.

Why is there two weeks added on?

The calculators count from the start of your last period, so when you conceive (approx two weeks later) you are automatically 'two weeks' pregnant. They can sometimes readjust your dates at later scans.

Loving your username btw 😂 guessing you didn't stick to that method!

Weeks pregnant is calculated from the first day of your last period. So your due date is 40 weeks from the first day of your period although you aren't actually pregnant for the first two weeks. It may be adjusted slightly at your dating scan.

They count it from went the egg started to mature and release.
So text book 28 day cycle

Day1 Egg starts to mature
Day 14 Ovulation - egg release - most fertile time
Day 21 Egg implants if fertile
Day 28 Positive test / Period

Unless you have ivf you can't be totally certain of when you conceived - sperm can hang around for a while and the baby can implant late etc. So until you have a dating scan the most accurate way to date for the general population is to go from the last period date.

I assume it stems from the days before scans when the only thing you knew for certain was when your last period was.

Most people know when their last period was whereas not everyone knows when they ovulated.

The system of dating was chosen decades ago and it would cause confusion and potentially dangerous medical errors if it was changed, also 40 is a nice round number. The benefits of changing it don't outweigh the risks of doing so, which is probably why we stick with it.

Though now I think about it, 35-40 weeks would be a nice easier way to think about term pregnancies compared to 37-42 weeks.