🤰 Pregnancy Due Date Calculator

Estimate your delivery date, gestational week and trimester — private, no login

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How Is the Pregnancy Due Date Calculated?

Our due date calculator uses Naegele's rule, the standard method recommended by ACOG (American College of Obstetricians and Gynecologists) and used worldwide:

Estimated Due Date (EDD) = First day of last menstrual period (LMP) + 280 days (40 weeks)

The 280-day figure assumes a 28-day cycle with ovulation on day 14. If your cycles are longer or shorter, the actual conception date shifts. The calculator also estimates:

Estimated conception date — LMP + 14 days
Current gestational week — weeks and days since LMP
Current trimester — 1st (weeks 1–12), 2nd (weeks 13–26), 3rd (weeks 27–40)
Days remaining until your estimated delivery date

The Three Trimesters of Pregnancy

First Trimester (Weeks 1–12)

The most critical period for organ development. The neural tube, heart, limbs and facial features form. Common symptoms include nausea ("morning sickness"), fatigue, breast tenderness, and frequent urination. Most miscarriages occur in this trimester.

Second Trimester (Weeks 13–26)

Often called the "honeymoon" trimester. Nausea typically fades, energy returns, and you may feel the first fetal movements (quickening) between weeks 16–25. The anatomy scan ultrasound is usually done at 18–22 weeks.

Third Trimester (Weeks 27–40)

The baby gains the most weight and the lungs mature. Expect Braxton-Hicks contractions, heartburn, swelling, and difficulty sleeping. Most providers recommend weekly check-ups from week 36.

How Accurate Is the Due Date?

Statistically, only about 5% of babies are born on their exact due date. Most arrive within two weeks before or after. The calculation is an estimate, not a deadline.

For the most accurate dating, a first-trimester ultrasound (between 7 and 13 weeks) measuring the crown-rump length (CRL) is considered the gold standard. If your LMP date and ultrasound date differ by more than 5–7 days in the first trimester, your doctor may adjust the due date based on the ultrasound.

If you have irregular cycles

Naegele's rule assumes a 28-day cycle. For longer cycles, ovulation (and conception) occurs later, so the due date should shift later. Roughly: adjusted EDD = LMP + 280 + (cycle length − 28) days. An early ultrasound is the most reliable option.

Other Ways to Calculate the Due Date

LMP method (Naegele's rule) — what this calculator uses; best for women with regular 28-day cycles
Conception date method — if known exactly, EDD = conception date + 266 days
IVF transfer date — EDD = transfer date + 263 days (Day 5 blastocyst) or + 266 days (Day 3 transfer)
First-trimester ultrasound — most accurate, ±5–7 days
Second-trimester ultrasound — ±10–14 days accuracy

Frequently Asked Questions

How is the due date calculated?

We use Naegele's rule: estimated due date = first day of last menstrual period (LMP) + 280 days (40 weeks). This is the standard method recommended by ACOG (American College of Obstetricians and Gynecologists).

How accurate is the due date?

Only about 5% of babies are born on their exact due date. Most arrive within two weeks before or after. First-trimester ultrasound is more accurate for dating.

What if I have irregular cycles?

Naegele's rule assumes a 28-day cycle. With longer cycles, ovulation and conception happen later, so the due date should be adjusted: add (cycle length − 28) days. An early ultrasound provides the most reliable dating.

Can the due date change?

Yes. If a first-trimester ultrasound gives a date more than 5-7 days different from your LMP date, your doctor may adjust your due date. After the first trimester, due dates are rarely changed.

What is full-term pregnancy?

ACOG defines: early term (37 weeks 0 days - 38 weeks 6 days), full term (39 weeks 0 days - 40 weeks 6 days), late term (41 weeks 0 days - 41 weeks 6 days), and postterm (42 weeks and beyond). Babies born full-term have the best outcomes.

Medical Disclaimer

This due date calculator is for general reference only and does not constitute medical diagnosis or treatment advice. Individual factors such as irregular cycles, IVF, or pregnancy complications may affect accuracy. Always consult your obstetrician or midwife for personalized pregnancy care. See our full disclaimer.

References

ACOG — Methods for Estimating the Due Date (Committee Opinion 700)
CDC — Maternal and Infant Health
NHS — Pregnancy and baby guide
WHO — Maternal health