How accurate are dates purely on a scan? Mine differ by 1 month and one day...

[LadyOfWaffle]

According to LMP I am due 7th July, had alot of confusion over the tests as to whether they were evapouration lines or +'s, eventually when missed second period got a clear +. The dates by the scan say I am due 8th August, but the 20 week scan they said the baby is big - could that mean it's older than they said it was? Should I be thinking 7th July- 8th August as my due date or are the scanning dates really accurate? I am so much bigger than last time and really uncomfortable and worried that I am due nearly a month earlier than I think so panicing abit!

if it helps i was told my EDD was december 9th by a doctor at confirmation of pg. I knew that wasnt possible. I ended up having an emergnacy scan and was given a new due date of november 5th. DS was born on novemeber 8th

even though your lmp was a certain date you could of concieved at the end of your cycle
thats what happenend to me this time

but my baby is bigger than there dates to and now they want to induce me 3 weeks early
back to my original date
how suprising