Pregnancy Due Date Calculator
Calculate your estimated due date, current week of pregnancy, trimester, and key milestones from your last menstrual period, conception date, or ultrasound.
Frequently Asked Questions
How is a pregnancy due date calculated?
Naegele's Rule is the standard method: add 280 days (40 weeks) to the first day of your last menstrual period (LMP). This assumes a regular 28-day cycle with ovulation on day 14. For cycles longer or shorter than 28 days, the due date shifts accordingly — add the difference. An early ultrasound (before 14 weeks) provides the most accurate dating based on foetal measurements (Crown-Rump Length).
How accurate is the estimated due date (EDD)?
Very few babies arrive exactly on their EDD — only about 4–5%. About 80% of babies are born within 2 weeks either side. The safe "full term" window is 37–42 weeks; births before 37 weeks are preterm. After 41 weeks, healthcare providers typically recommend induction. The EDD is a planning tool, not a precise prediction.
What are the three trimesters of pregnancy?
First trimester: weeks 1–12 — organ formation, most sensitive period for birth defects, miscarriage risk highest. Second trimester: weeks 13–27 — often the most comfortable, baby's sex visible on scan around week 20, quickening (first movements) typically felt at weeks 16–20. Third trimester: weeks 28–40+ — rapid growth, baby's position shifts, lungs mature around 34–36 weeks.
What key milestones should I expect during pregnancy?
Week 4–5: positive pregnancy test. Week 8–12: first prenatal appointment, heartbeat detected by ultrasound. Week 12: nuchal translucency (Down syndrome) scan. Week 16–20: anatomy scan, sex can be confirmed. Week 24: viability threshold (survival outside womb possible with intensive care). Week 28: third trimester begins, gestational diabetes screening. Week 36–37: weekly monitoring begins.
Can I calculate due date from conception date or ultrasound?
Yes. From conception: add 266 days (38 weeks) rather than 280 — because conception typically occurs 14 days after LMP. From ultrasound dating: your sonographer calculates gestational age from the Crown-Rump Length (CRL) in the first trimester, or head/abdominal circumference in the second trimester. NHS and ACOG recommend using the first ultrasound date if it differs by more than 7 days from LMP dating.