Pregnancy due date calculator

Pregnancy is dated from the first day of your last menstrual period, about 2 weeks before actual conception. At "4 weeks pregnant," the embryo has only existed for about 2 weeks. This convention exists because most people know when their period started but not when they ovulated.

Early term: 37+0 to 38+6 weeks. Full term: 39+0 to 40+6 weeks. Late term: 41+0 to 41+6 weeks. Post-term: 42+0 and beyond. Babies born at 39-40 weeks have slightly better outcomes than those born at 37-38 weeks.

Early in pregnancy, embryos grow at consistent rates, making ultrasound highly accurate. Later, natural variation in fetal size increases. First trimester ultrasound dates within 3-5 days; third trimester within 2-3 weeks. This is why due dates aren't changed based on late ultrasounds.

Your healthcare provider will use ultrasound to estimate gestational age at your first prenatal visit. Early ultrasound is very accurate. Providers are accustomed to working with uncertain dates.

For someone with regular 28-day cycles who remembers their LMP precisely, LMP-based dating is typically accurate within 1-2 weeks. Early ultrasound is more accurate, within 3-5 days. Since only 5% of babies arrive on the exact due date, think of it as the center of a range.

Your provider might adjust after early ultrasound if measurements differ significantly from LMP dating. Once established (usually by end of first trimester), the due date typically stays fixed. Dates aren't changed based on third trimester ultrasounds.

Common, especially for first pregnancies. Your provider will monitor more closely with additional appointments. Most providers recommend inducing by 41-42 weeks to reduce risks associated with post-term pregnancy.