Pregnancy Due Date Calculator

Estimation of due date

The due date, also known as the estimated date of confinement, is an estimation of when a pregnant woman will deliver her baby. While the due date is often estimated as a single date, it can be helpful to consider a range of due dates, since only 4% of births occur on the exact estimated due date.¹

Due dates can be estimated using a number of different methods, including the last menstrual period, ultrasound, conception date, and IVF transfer date.

Last menstrual period

The default for this calculator bases the calculation on a woman's last menstrual period (LMP), under the assumption that childbirth on average occurs at a gestational age of 280 days, or 40 weeks. Although there is some debate regarding when pregnancy technically begins, gestational age does not vary since it is based on LMP. Thus, the due date is usually estimated by calculating the date that is 40 weeks from the start of a woman's LMP.

Ultrasound

Estimating due date based on ultrasound involves the use of soundwaves to look inside the body and compare the growth of the fetus to typical growth rates of babies around the world. It is a safe process that can provide an accurate estimate of the due date early in the pregnancy.

In vitro fertilization (IVF)

When using in vitro fertilization, the estimation of the due date is generally more precise than calculating the due date based on natural conception, since the exact transfer date is known. It still uses the average gestational age at birth of 40 weeks, factoring in the date of the 3-day or 5-day embryo transfer.

Due date as a reference point

Generally, the point within the 37 to 42-week window at which the baby is born is not a cause for concern. Babies born between 37-39 weeks, 39-41 weeks, and 41-42 weeks are considered early term, full-term, and late-term, respectively. Under normal circumstances, babies born within any of these ranges can be healthy, though full-term babies generally have better outcomes.²