Pregnancy Due Date Calculator

How to use this tool

Choose your input method. Select LMP, conception date, ultrasound, or IVF transfer.
Enter the date. Input the relevant date, cycle length or ultrasound gestational age when applicable, and embryo age for IVF.
View results. Your estimated due date, current gestational age, trimester, and key milestones are displayed.

How the due date is calculated

The most common method is Naegele's rule: add 280 days (40 weeks) to the first day of the last menstrual period. This assumes a standard 28-day cycle and ovulation on day 14. If your cycle length differs, the calculator adds or subtracts the difference.

Pregnancy milestones

Week 6–10: First prenatal visit and viability ultrasound.
Week 12–13: End of first trimester; nuchal translucency scan.
Week 18–20: Anatomy scan (anomaly scan).
Week 24: Fetal viability threshold. Survival outside the womb is possible with intensive care.
Week 37: Early term begins (37 weeks 0 days).
Week 39: Full term begins (39 weeks 0 days).
Week 40: Estimated due date.
Week 41: Late term begins.
Week 42: Postterm begins. Discuss care and timing with your healthcare professional.

Gestational age vs. fetal age

Gestational age is counted from the last menstrual period, which means the fetus is typically about 2 weeks younger than its gestational age. A 12-week gestational age corresponds to approximately 10 weeks of actual fetal development.

Trimester summary

Trimester	Weeks	Key milestones
First	1–13	Implantation; heart begins beating (~week 6); all major organs start forming; nuchal translucency scan (week 12–13)
Second	14–27	Fetal movement felt (~week 18–20); anatomy scan; sex can often be determined; viability threshold reached (~week 24)
Third	28–40	Rapid weight gain; lung maturation; full term begins at week 39; estimated due date at week 40

Ultrasound dating

A first-trimester ultrasound is the most accurate ultrasound method for establishing or confirming gestational age. Later scans still provide important growth information, but their dating accuracy decreases as pregnancy advances. Whether a scan should change an estimated due date depends on gestational age, the measurement, and the clinical history; a general calculator cannot make that clinical decision. See the ACOG guidance on estimating the due date .

IVF transfer dating

For IVF pregnancies, due-date estimates use both the transfer date and the embryo’s age on transfer day. This calculator uses 263 days after a day-3 transfer or 261 days after a day-5 transfer, following ACOG’s assisted-reproductive-technology dating examples. Select the embryo age recorded by your clinic and confirm your official estimated due date with your healthcare professional.

Trimester and term labels

This calculator uses common gestational-week bands: the first trimester runs through 13 weeks 6 days, the second from 14 weeks 0 days through 27 weeks 6 days, and the third from 28 weeks 0 days through 40 weeks 6 days. ACOG further distinguishes early term (37 weeks), full term (39 weeks), late term (41 weeks), and postterm (42 weeks). These labels describe gestational-age ranges; they do not recommend a delivery date. See the ACOG definitions of term pregnancy .

How common is delivery on the due date?

Only about 5% of babies are born on their exact due date. Approximately 80% of births occur within two weeks either side of the EDD (between 38 and 42 weeks). The due date is best understood as the center of a normal distribution, not a deadline.

This calculator is for general information and is not medical advice. Consult a healthcare professional for personalized guidance.

Frequently asked questions

How is the due date calculated from the last menstrual period?

Naegele's rule: add 280 days (40 weeks) to the first day of your last menstrual period. This assumes a 28-day cycle with ovulation on day 14. If your cycle is longer or shorter, the calculator adjusts the due date accordingly.

How accurate is an estimated due date?

Only about 5% of babies are born on their exact due date. Approximately 80% are born within 10 days either side. Early ultrasound (before 14 weeks) is the most accurate dating method.

What are the three trimesters?

This calculator groups gestational age into the first trimester through 13 weeks 6 days, the second trimester from 14 weeks 0 days through 27 weeks 6 days, and the third trimester from 28 weeks 0 days through 40 weeks 6 days. ACOG defines early term as 37 weeks 0 days through 38 weeks 6 days, full term as 39 weeks 0 days through 40 weeks 6 days, late term as 41 weeks 0 days through 41 weeks 6 days, and postterm from 42 weeks.

How is the IVF due date calculated?

The estimate uses the transfer date and embryo age. A day-3 transfer adds 263 days; a day-5 transfer adds 261 days. Confirm the embryo age and estimated due date with your fertility clinic.