Girls, we're being put in the hospital for a planned delivery. And the…

Girls, we're being put in the hospital for a planned delivery. And the first strangeness: at the consultation, the doctor I was seeing and who did an ultrasound, said my due date is 40 weeks and 4 days. In the hospital today they said it's 40 weeks and 1 day. They said there's some formula by which they calculate it. Now I'm thinking, who's wrong and am I going into labor or not??