To anyone who used a pregnancy calculator when you found out that you were pregnant, based off of day 1 of your last cycle, how accurate was the calculator when you went to your first US? Was it off by a week or more? Was it spot on? I'm getting my first ultrasound May 16th and I am wondering if I should expect my due date to be completely different. I should be about 9 weeks when I get it done. Thanks!