Pregnancy Due Date Calculator

--Estimated Due Date
--Current Pregnancy Week
--Trimester

Important Pregnancy Milestones

WeekMilestoneEstimated Date

Disclaimer: This calculator provides estimates only. Always consult a qualified healthcare professional or obstetrician for medical advice and accurate pregnancy dating.

How Is a Pregnancy Due Date Calculated?

The most common method for estimating a baby's due date is Naegele's Rule, named after German obstetrician Franz Karl Naegele. The formula adds 280 days (40 weeks) to the first day of the last menstrual period (LMP). This accounts for both the two weeks before ovulation and the 38 weeks of actual fetal development from conception.

Understanding Pregnancy Trimesters

  • First Trimester (Weeks 1–12): Rapid embryonic development. Morning sickness and fatigue are common. Miscarriage risk is highest. The 12-week nuchal translucency (NT) scan screens for chromosomal conditions.
  • Second Trimester (Weeks 13–27): Often called the "golden trimester" — most symptoms ease and energy returns. The 20-week anatomy scan checks fetal development in detail.
  • Third Trimester (Weeks 28–40+): Rapid weight gain for both mother and baby. Preparations for birth begin. Full term is considered 37–40 weeks.

LMP vs Conception Date

If you know your conception date (e.g., from IVF or tracking ovulation), the due date is calculated as conception date + 266 days (38 weeks). The LMP method is more widely used because the exact day of conception is often unknown, whereas the LMP is easier to identify.

When Do Doctors Adjust the Due Date?

An early ultrasound (before 14 weeks) measuring crown-rump length (CRL) provides the most accurate dating. If the ultrasound measurement differs from LMP-based dating by more than 5–7 days, obstetricians will typically revise the estimated due date accordingly.

Medical Disclaimer: This tool is for informational purposes only. Only 5% of babies are born exactly on their due date. Always follow the guidance of your healthcare provider for all pregnancy-related decisions.

Frequently Asked Questions

How accurate is a due date calculator?
Due date calculators are estimates. Only about 5% of babies arrive on their predicted due date. Most births occur within 2 weeks before or after the estimated date. An early ultrasound is the most accurate dating method.
What is the full term pregnancy period?
A full-term pregnancy is defined as 39–40 weeks. Babies born at 37–38 weeks are "early term," at 41 weeks are "late term," and at 42+ weeks are "post-term." The majority of deliveries occur between weeks 38 and 42.
What if my cycles are irregular?
Naegele's Rule assumes a 28-day cycle with ovulation on day 14. If your cycles are longer or shorter, your doctor may adjust the due date after an early ultrasound measurement.
Can I calculate the due date from an IVF transfer?
Yes. For a 5-day blastocyst transfer, add 261 days to the transfer date. For a 3-day embryo transfer, add 263 days. Your fertility clinic will confirm the exact calculation.