The Due Date Calculator estimates the delivery date of a pregnant woman based on her last menstrual period (LMP), ultrasound, conception date, or IVF transfer date.

Due Date Calculator

Enter the first day of your last menstrual period (LMP) to calculate estimated due date (EDD).

LMP date

Or pregnancy age

Note: This is an estimate (typical pregnancy = 280 days / 40 weeks from LMP). For medical advice, consult your healthcare provider.

Due Date Estimation

🩷 Estimation of Due Date

The due date, or estimated date of confinement, predicts when a pregnant woman is likely to deliver. While often presented as a single date, it is helpful to consider a range of due dates, since only about 4% of births occur exactly on the estimated day.

Methods to Estimate Due Date

1. Last Menstrual Period (LMP)

The default method in most calculators uses a woman’s last menstrual period (LMP). Childbirth is assumed to occur at a gestational age of 280 days (40 weeks). Although pregnancy may technically begin at fertilization or implantation, gestational age is calculated from LMP. Most pregnancies last between 37–42 weeks, making 40 weeks a common estimate for due date calculations.

2. Ultrasound

Ultrasound uses sound waves to measure fetal growth and compare it with typical global growth patterns. Early pregnancy ultrasounds can provide an accurate due date, and this method has no known risks to the baby.

3. Conception Date

Calculating due date based on the exact conception date is similar to using LMP. There is typically a 2-week difference between the two methods because conception occurs after the start of the LMP.

4. In Vitro Fertilization (IVF)

IVF provides the most precise due date estimate because the embryo transfer date is known. The calculation may also consider LMP, ovulation, egg retrieval, insemination, or the 3- or 5-day embryo transfer date.

Due Date as a Reference Point

Babies born between 37–42 weeks are usually healthy. The timing is classified as:

Early term: 37–39 weeks
Full term: 39–41 weeks
Late term: 41–42 weeks

Preterm: before 37 weeks | Postterm: after 42 weeks. These ranges help doctors determine if interventions are necessary.

For example, labor before 37 weeks may require stopping contractions to avoid complications, while labor after 42 weeks may require induction. The placenta may stop functioning properly if the pregnancy extends too long, affecting nutrient and oxygen supply to the baby.

References

1. Moore, Keith. 2015. "How accurate are 'due dates'?" BBC, February 3, 2015. bbc.com
2. Wikipedia: The Free Encyclopedia. 2017. wikipedia.org
3. PubMed Health. 2014. "Pregnancy and birth: When your baby's due date has passed." ncbi.nlm.nih.gov