Pregnancy due date ultrasound or LMP which is accurate? Note: Ultrasound is more accurate, due date more than 7 days different use ultrasound (because of irregular periods) ultrasound performed in the first trimester (up to 13 weeks and 6 days) is generally considered more accurate than relying solely on the last menstrual period (LMP), LMP Accuracy: 28days ovulation … [Read more...] about pregnancy calculator by LMP vs ultrasound