How did y’all figure out your due dates?

Crystal

When I went in for my 1st and so far only ultrasound (I was about 8 weeks), the nurse said I was measuring a week behind. Dr said to keep the same due date, but nurse said to change it. I don’t know how far alone I am right now. The app tells me 14 weeks 6 days. Last menstrual pd was August 12.