Why does my gestational age on sonogram date back to april 15th when my lmp was march 24th? (i have a due date of january 13 it was around december 30

Ultrasound accuracy: Ultrasounds are only accurate plus or minus two weeks for estimating gestational age of pregnancy.

Date Changes: An early ultrasound is very accurate for dating a pregnancy. Sometimes it is more accurate than a woman's memory of her periods. Also sometimes bleeding in early pregnancy can be confused with a period. Because of this, an ultrasound can change your due date. If you calculate back to an LMP using the new u/s due-date it will change your LMP also. Best wishes!