How far off could ultrasound be?

[JNMA88]

Ok, going off last menstrual cycle my due date is February 26th. At my first appointment my OB ordered an ultrasound to get an accurate measurement. I just got a call earlier today that based on the ultrasound my due date is March 9th. Something just isn't adding up in my book; if that was right I wouldn't have conceived until several days after I got a positive test at home (I keep notes on almost everything regarding my health, and I did the math). My cycle before this pregnancy was like clockwork and I'm just not seeing how there could be almost a 2 week discrepancy. Has anyone else had something like this happen or am I just over thinking this?

[lisasmall22285]

The scans work on size of baby at time of scan. They quite often are off. Either before or after. Babies don't all come on due date anyway. It is just a rough date. I wouldn't stress too much

[SnowBunny3]

The scan dont usually be off...probably by couple days added on or even taking off but the date they gave it..if it isnt tht date the date for your baby to be born is near to tht.