Due Date Calculator
Enter your last period date or conception date to find your estimated due date, current pregnancy week, and trimester in seconds.
Calculate Your Due Date
Assumes a standard 28-day cycle with ovulation on Day 14
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How Your Due Date is Calculated
The estimated due date (EDD) is calculated by adding 280 days (40 weeks) to the first day of your last menstrual period. This is called Naegele's Rule — the standard formula used by obstetricians worldwide. The formula assumes a 28-day cycle with ovulation on Day 14.
Why Is Pregnancy Counted from LMP?
It seems counterintuitive to count pregnancy from your period — before conception has even occurred. The reason is practical: most people know when their last period started, but very few know their exact conception date. The LMP date is a reliable reference point that correlates well with fetal development on ultrasound.
How Accurate Is the Due Date?
Only about 4% of babies are born on their exact due date. Most babies arrive within 2 weeks before or after the EDD. Your due date is best understood as the center of a 5-week window (38 to 42 weeks) rather than a precise date. An ultrasound between 10 and 14 weeks is the most accurate way to confirm or adjust your due date.
Key Pregnancy Milestones to Watch
- Week 6–8: First prenatal appointment, heartbeat may be detectable
- Week 10–13: First trimester screening, NIPT/nuchal translucency scan
- Week 18–20: Anatomy scan (20-week scan) — gender visible if desired
- Week 24–28: Glucose tolerance test (GDM screen), anti-D injection if Rh-negative
- Week 36: Weekly appointments begin, baby positions for birth
- Week 39–40: Full term — most providers won't let pregnancy continue beyond 42 weeks