due dates

Allison
How many of your doctors gave you your due date off of the first day of your last menstural cycle? 
If you could not figure out when your last first day was how far along were you when you got a dating scan? 
Do any of you know when your last first day was and you got a completely different due date than what your doctor has given you?
And if you have already given birth did you deliver close to your due date from your docto or if you guessed your own was it closer to the due date you predicted?