How do they calculate due date?

Question

I was on the phone with the nurse to set up my first pre natal appointment and she said our baby would be due around March 19th, but my last period was June 12th and she said I'm already four weeks!? I'm so confused 🤷🏼‍♀️ I'm a first time mom so I was just wondering if anyone had any insights!

Answer

Hi! It's because we don't actually know what Day conception happened. So they go by last period. Once you go to ultrasound they will pinpoint it a little better.

Answer

They base it on your LMP at first, then when they do the ultrasound, they're able to measure the baby's CR (crown to rump) and they'll give you a more approximate estimated due date. It could be later than you initially thought because it all depends on when you ovulated. 
I went to my first appointment at 7w based on my LMP, but baby measured at 5w6d so that is what we are going off of.
Hope this helped!

Answer

1) Take the day you started your last period
2) Add 7 days 
3) 'Subtract' 3 months 
So if your last period started June 12, add 7 days to get June 19, and subtract 3 months = March 19th! 
It's a tool that doesn't require knowing your exact ovulation date, so it's just an estimation.

How do they calculate due date?

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