Pregnancy Due Date Calculator

Frequently Asked Questions

• How is the due date calculated?

  Naegele's rule: LMP + 280 days (40 weeks). Conception date + 266 days. IVF transfer date adjusts for embryo age (3-day or 5-day blastocyst).

• How accurate is the LMP method?

  Reasonably accurate for women with regular 28-day cycles. Less accurate with irregular cycles or unsure LMP. Ultrasound dating in the first trimester is the most reliable.

• When is conception?

  Conception typically occurs ~14 days after the start of LMP (around ovulation). Calendar of pregnancy is dated from LMP, so you're considered "2 weeks pregnant" at the moment of conception.

• How do trimesters work?

  First: weeks 1-13. Second: weeks 14-27. Third: weeks 28-40. Each trimester has its own milestones, screenings and considerations.

• What if my cycle isn't 28 days?

  Adjust ovulation/conception date forward or backward by the difference. The LMP method assumes a 28-day cycle; some calculators offer "cycle length" adjustment.

• Are early pregnancy symptoms reliable for dating?

  No — symptoms vary widely between women and pregnancies. Use LMP, conception date or ultrasound for accurate dating.

• How accurate are due dates?

  Only ~5% of babies arrive on the exact due date. Normal full-term delivery is anywhere from 37-42 weeks. The due date is a target, not a deadline.

• What is gestational age vs fetal age?

  Gestational age is measured from LMP (the standard). Fetal age (since conception) is ~2 weeks less. Doctors use gestational age throughout.

• When should I see a doctor?

  Schedule your first prenatal visit around 8-10 weeks gestational age. Earlier if you have medical conditions, prior complications or symptoms of concern.

• Can stress affect due date?

  Severe stress is associated with marginally higher rates of preterm birth, but the calculated due date remains unchanged. The calculation reflects biology, not lifestyle.