In UK they change the due date based on what the ultrasound says when you have it not when your lmp says. My LMP put me 3 weeks ahead of my due date because i have really long cycles. I told the doc i knew when i ovulated and conceived but he had to go by lmp until the ultrasound proved otherwise then they changed my due date. The reason they are different could be because you ovulated earlier or later than usual in your cycle and as its only 4 days difference i wouldn't worry too much.
The baby will come whenever the baby wants anyway:) and the due date is just an estimate so I wouldn't worry about it :)
i was measuring a few days a head like 4 days so my doctor wants to go by my last LMP too. and my due date is august 11th but if she went by ultrasound it would make it august 7th
Based on your last posts I'm assuming you're around 13 and a half weeks? I'm not sure what you mean by the doctor told you, you look a few days ahead. They would by no means be able to determine anything by looks. As for ultrasound if you had a first trimester ultrasound (before 13 weeks) that would be the most accurate for dating since if they are off at most only a week but usually only a day or so. If your lmp and ultrasound show dates that are almost exact then they will probably keep it at the lmp for dating. In the end though it doesn't really matter if its a couple days different because it is an ESTIMATED due date. You could deliver a couple weeks early or even a week or so later and it isn't going to make really any difference. People rarely and I mean very rarely give birth on their due date.