Pregnancy Due Date Calculator

The Formula

The Estimated Due DateThe estimated date of delivery, typically calculated as 280 days (40 weeks) from the first day of the last menstrual period. is calculated by adding 280 days (40 weeks) to the first day of the Last Menstrual Period. Cycle length adjustment shifts ovulation timing accordingly. IVF dates use embryo-specific offsets: Day 5 blastocyst transfer + 261 days, Day 3 transfer + 263 days.

Variable Definitions

How to Use This Calculator

1. 1

   Select your calculation method — LMP (last period) is the most common clinical standard.

2. 2

   Enter the relevant date in YYYY-MM-DD format.

3. 3

   If using LMP and your cycle is not 28 days, enter your average cycle length for accuracy.

4. 4

   If using IVF, select the appropriate method and enter your transfer date.

5. 5

   Review your due date, current gestational age, trimester start dates, and key milestones.

6. 6

   Share the results with your healthcare provider for clinical confirmation at your first ultrasound.

Common Applications

• Pregnancy planning — establish the estimated due date (EDD) from LMP or conception date for prenatal appointment scheduling and trimester planning
• Gestational age tracking — determine current weeks pregnant and remaining days to due date for monitoring fetal development milestones
• Cycle length adjustment — for women with cycles that differ from 28 days, get a personalized due date that accounts for ovulation timing differences
• IVF pregnancy dating — calculate due dates for Day 3 and Day 5 embryo transfers using the appropriate embryo-specific offsets for assisted reproduction

EDD is calculated as LMP + 280 days (Naegele's Rule); full term spans weeks 37-42

Understanding the Concept

The Estimated Due DateThe estimated date of delivery, typically calculated as 280 days (40 weeks) from the first day of the last menstrual period. uses Naegele's Rule: LMP + 280 days. This formula was developed by German obstetrician Franz Naegele in the early 1800s and remains the standard dating method today. Only about 5% of babies are born on their exact due date — most arrive within 2 weeks on either side, which is why healthcare providers refer to a <<due month>> rather than a specific day. First-trimester ultrasound (crown-rump length measurement at 8–13 weeks) provides the most accurate dating, especially for women with irregular cycles or uncertain LMP. The three trimesters mark distinct phases: the first trimester involves organ formation and carries the highest miscarriage risk; the second trimester brings fetal movement and most prenatal screening tests; the third trimester involves lung maturation, rapid weight gain, and preparation for delivery. Normal delivery is defined as 37–42 weeks. Babies born before 37 weeks are preterm, while those after 42 weeks are post-term. If your due date changes after an ultrasound, the earlier dating (usually the ultrasound) is considered more reliable.

Frequently Asked Questions

Sources & References