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Estimated Delivery Date (EDD)

Due Date Calculator

Estimate when your baby may arrive using Naegele's standard obstetrical formula.

Due Date Calculator

Find your estimated arrival date based on the standard medical 280-day gestational rule.

The first day of bleeding in your last cycle before becoming pregnant.
Your Estimated Due Date
Wednesday, May 26, 2027
Approximately 238 days from today
Current Gestational Age
6 weeks
Week 7 of 40
Current Trimester
First Trimester
Weeks 1–13
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How this is calculated: This calculator uses Naegele's Rule, the standard clinical dating standard. It adds 280 days (40 weeks) from the first day of your last period. While useful for planning, remember that only about 4–5% of babies arrive on their exact calculated due date.

How Is Your Due Date Calculated?

1. The 280-Day Obstetrical Standard (Naegele's Rule)

In standard clinical medicine, a full pregnancy is counted as 40 weeks (280 days) starting from the first day of your last normal menstrual period (LMP). This formula was introduced by German obstetrician Franz Karl Naegele in the 19th century and remains the foundation of global obstetrics today.

Estimated Due Date = First Day of LMP + 280 Days (40 Weeks)

2. Why Is Gestational Age Counted From Your Period?

Ovulation and conception usually happen roughly two weeks after your period starts. However, because exact conception dates are rarely known with pinpoint certainty, healthcare providers universally reference the first day of your last cycle to ensure consistent clinical records and ultrasound timelines.

3. Due Dates Are Estimates, Not Deadlines

A due date represents the estimated 40-week milestone. In reality:

  • Only about 4% to 5% of infants are born on their exact calculated due date.
  • Approximately 80% of healthy infants arrive within a two-week window before or after the estimated date (between 38 and 42 weeks).
  • Your obstetrician or midwife will review your early ultrasound measurements (typically the 8–12 week dating scan) to confirm or adjust your official clinical due date.
Common Questions

Pregnancy Calculation FAQ

Reliable, evidence-based answers to frequently asked questions about gestational dating and timelines.

How is a pregnancy due date calculated?
Medical providers calculate estimated due dates using Naegele's rule: by adding 280 days (40 weeks) to the first day of your last normal menstrual period (LMP). If your menstrual cycle is regularly longer or shorter than the standard 28-day model, the calculation can be adjusted accordingly.
How many weeks is a full-term pregnancy?
A full-term pregnancy is generally considered 40 weeks (280 days) from your LMP. Medical guidelines classify babies born between 37 weeks and 38 weeks and 6 days as 'early term', between 39 weeks and 40 weeks and 6 days as 'full term', and 41 weeks to 41 weeks and 6 days as 'late term'.
How are pregnancy weeks counted?
Pregnancy weeks describe completed weeks plus extra days. For example, if you are at '12 weeks, 3 days', you have completed 12 full weeks and are currently experiencing your 13th week of pregnancy.
What is the difference between gestational age and conception age?
Gestational age is measured from the first day of your last period, before ovulation and fertilization actually occur. Conception age (fetal age) begins at the moment the egg is fertilized, which typically takes place approximately 14 days after your period. Gestational age is standard in medical obstetrics.
Can my healthcare provider give me a different due date?
Yes, and this is completely normal. An early first-trimester ultrasound dating scan (crown-rump length measurement) provides the most precise estimate of fetal development. If there is a notable discrepancy between your LMP date and the ultrasound measurement, your clinician will update your official estimated due date.
How accurate is an estimated due date?
Only about 4% to 5% of babies arrive precisely on their estimated due date. It is best considered an estimated arrival window; roughly 80% of healthy infants are born within a two-week window before or after the estimated date.