I was measuring a week ahead and they changed it only cause it made sense with my short cycles. Otherwise they don't normally change it

not unless your doctor gives you a new due date

Yeah in the beginning they said I wasn't as far as long as I thought I was by my last period. But yesterday I was measuring 21 weeks which makes sense to when my last period was. Thanks! @raising_carson16

your due date stays the same

I always measured about 2 weeks bigger. go by your last period of possible. when they do the ultrasound they can tell you exactly how far you are