About Pregnancy Due Date Calculator

Calculate estimated due date (EDD), current week, and pregnancy milestones. Part of the DevTools Surf developer suite. Browse more tools in the Calculators collection.

Use Cases

• Calculate EDD from last menstrual period for initial prenatal planning.
• Track which trimester and week you are in to align with prenatal appointment schedules.
• Determine fetal development milestones by gestational week.
• Adjust EDD calculations when ultrasound dates differ from LMP-based estimates.

Tips

• The standard Naegele's Rule (LMP + 280 days) assumes a 28-day cycle — adjust for longer cycles by adding extra days beyond 28.
• Track gestational age in weeks-and-days format (e.g., 12w3d) to match clinical ultrasound reports exactly.
• Use the conception date input if you know it from IVF or ovulation tracking — it is more accurate than LMP for irregular cycles.

Fun Facts

• Naegele's Rule for estimating due dates was formulated by German obstetrician Franz Karl Naegele in 1812 and remains the basis for most EDD calculations today.
• Only about 4% of babies are born on their predicted due date; 80% are born within 2 weeks before or after.
• The average human gestation is 280 days (40 weeks) from LMP, but a 2013 study published in Human Reproduction found natural variation of 37 days among uncomplicated pregnancies.

FAQ

Is the due date accurate?

The EDD is an estimate with a +/- 2-week clinical margin. Early ultrasound (before 12 weeks) is the most accurate dating method and may override the LMP-based calculation.

What is gestational age vs. fetal age?

Gestational age counts from the first day of the last period (about 2 weeks before conception). Fetal age (embryonic age) counts from conception. Clinicians use gestational age.