(For example, if someone computes a due date by counting forward from her last period, it can be way off if her periods are not regular, and counting back from it 266 days to a presumed conception date
would be equally useless. Computing a conception date based on
an ultrasound later in pregnancy could be way off also, because babies grow at different rates.) Your original question didn't include how you had gotten the due date or when, so I asked.