If i conceived on march 23rd why is my confirmed due date december 10th?

Due date is estimate: Your due date using the date of conception (if you are absolutely sure of it) is December 14th. The December 10th date was probably estimated based on the first day of your last period, which is slightly less accurate, or the measurements of the baby on ultrasound, which might be a bit more or less accurate depending on how early the scan was done. Due dates are +/- up to two weeks!