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The Vatsalyam

Maternal & Child Health
Free Pregnancy Health Tool

Pregnancy Due Date Calculator

Estimate your expected date of delivery (EDD), current gestational age, trimester, term category and key pregnancy dates using LMP, ultrasound dating or IVF/ART transfer dating.

LMP & 40-Week Dating Ultrasound Dating IVF / ART Dating Gestational Age Mobile Friendly

Calculate Your Due Date

Select the dating information you have. For clinical care, the obstetric dating method documented by your healthcare professional should be followed.

Enter the first day of your most recent menstrual period.
Default is 28 days. The calculator optionally adjusts the estimate for a different cycle length.
Standard LMP dating: pregnancy is conventionally estimated as 280 days (40 weeks) from the first day of the LMP. A 28-day cycle is assumed for the standard calculation.
Use the date of the ultrasound used for pregnancy dating.
Example: 12 weeks 4 days = 12 in the first box and 4 in the second.
Dating principle: first-trimester ultrasound using fetal measurement is the most accurate ultrasound method for establishing or confirming gestational age. Later ultrasound dating is less precise.
Enter the actual embryo transfer date.
For ART pregnancies, use the embryo age and transfer date documented by the fertility clinic.
ART dating: for a Day-5 embryo transfer, the ACOG method corresponds to an EDD 261 days after transfer; for a Day-3 embryo transfer, 263 days after transfer.

Pregnancy Term Categories

The following categories help explain where a pregnancy falls by gestational age. They are different from the calculated EDD itself.

Category Gestational age Meaning
Preterm Less than 37+0 weeks Birth before 37 completed weeks.
Early term 37+0 to 38+6 weeks Term period before full term.
Full term 39+0 to 40+6 weeks Full-term gestational period.
Late term 41+0 to 41+6 weeks Late-term pregnancy.
Postterm 42+0 weeks or more Pregnancy at or beyond 42 completed weeks.

How Pregnancy Due Dates Are Calculated

A conventional LMP-based EDD is calculated as 280 days (40 weeks) from the first day of the last menstrual period. This convention assumes a 28-day menstrual cycle and approximately day-14 ovulation. Because menstrual dates and ovulation timing can vary, the LMP estimate is not equally reliable for everyone.

Ultrasound dating can establish or confirm gestational age, with first-trimester ultrasound being the most accurate ultrasound approach. For pregnancies resulting from assisted reproductive technology, the ART-derived gestational age is used rather than relying only on an LMP date.

Clinical dating principle: The calculator should not be used to independently override an EDD documented by the treating obstetrician, midwife or other qualified healthcare professional.

Pregnancy Due Date Calculator FAQ

How accurate is an LMP-based due date?
LMP dating is a useful starting point, but it assumes a regular 28-day cycle and predictable ovulation. Uncertain LMP dates, irregular cycles and variation in ovulation can reduce its accuracy. Ultrasound dating, especially in the first trimester, may provide a more accurate gestational-age assessment.
What is the standard pregnancy length?
The conventional obstetric estimate is 280 days, or 40 weeks, counted from the first day of the LMP.
Which ultrasound is best for pregnancy dating?
ACOG states that ultrasound measurement of the embryo or fetus in the first trimester, through 13 weeks 6 days, is the most accurate ultrasound method for establishing or confirming gestational age.
Can my due date change after an ultrasound?
It can be revised when the clinical criteria for redating are met. Once a best obstetric EDD has been established, repeated changes based on later scans are generally avoided unless there is an appropriate clinical reason.
How is an IVF due date calculated?
For ART pregnancies, dating is based on the embryo age and transfer date. Using the ACOG method, a Day-5 embryo transfer corresponds to an EDD 261 days after transfer, while a Day-3 embryo transfer corresponds to 263 days after transfer.
What if I do not know my LMP?
Do not guess the LMP. Your healthcare professional can use ultrasound dating or another clinically appropriate method. The WHO and ACOG guidance both recognize ultrasound as an important method for establishing gestational age.
Does the due date mean I will deliver on that exact day?
No. The EDD is an estimated date used for pregnancy dating and clinical planning. Delivery may occur before or after the estimated date.
What should I do if my calculated date differs from my ultrasound report?
Use the dating assessment documented by your treating healthcare professional. Do not independently switch between dates based only on an online calculator. The timing and type of ultrasound, LMP reliability and the clinical picture all matter when establishing the best obstetric EDD.

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Guideline references used for this calculator:
  • American College of Obstetricians and Gynecologists (ACOG), Methods for Estimating the Due Date, Committee Opinion No. 700.
  • World Health Organization (WHO), recommendations on antenatal care and ultrasound assessment before 24 weeks.
Medical information disclaimer: This calculator is intended for general health education and pregnancy-date estimation. It does not diagnose pregnancy complications, determine fetal health, replace an ultrasound examination, or replace antenatal care. If you have bleeding, severe abdominal pain, severe headache, reduced fetal movement, leaking of fluid, fever, seizures or another urgent pregnancy concern, seek prompt medical assessment.