Due date calculator

Use this due date calculator to estimate your baby’s arrival on your last period, conception date, or IVF transfer.

Related calculators:

Understanding your due date

The due date—also called the estimated date of delivery—is a projection of when a pregnant person is most likely to give birth. Although many calculators present this as a single calendar date, it is more realistic to think of it as a range. Only about 4% of babies are born exactly on their predicted due date, and most arrive within a few weeks before or after.

Ways to estimate a due date

There are several methods for calculating an estimated delivery date, including the last menstrual period (LMP), ultrasound measurements, conception date, and, in the case of assisted reproduction, the embryo transfer date.

Last menstrual period (LMP)

The most common approach—used by this calculator as the default—counts 280 days (40 weeks) forward from the first day of your last period. This is based on the typical length of a full-term pregnancy when measured as gestational age, which starts with the LMP rather than the actual date of conception. While pregnancies can last anywhere from 37 to 42 weeks, 40 weeks is generally used for planning purposes.

Ultrasound

Ultrasound technology uses sound waves to capture images of the developing baby. By measuring the fetus and comparing growth patterns to standard benchmarks, healthcare providers can estimate a due date—especially early in pregnancy—often with a high degree of accuracy. Ultrasound is non-invasive, quick, and has no known risks to the baby.

Conception date

If the exact day of conception is known, the due date can be calculated by adding 266 days (38 weeks) from that date. This method typically results in a due date about two weeks later than the LMP method, reflecting the time between the start of the period and ovulation.

In Vitro Fertilization (IVF)

For pregnancies achieved through IVF, the date of embryo transfer or fertilization is precisely known, making due date estimation more exact. Calculations may be based on the LMP, ovulation, egg retrieval, insemination date, or the day of a 3-day or 5-day embryo transfer. IVF timelines still assume an average gestational period of 40 weeks from the LMP equivalent.

Why the due date is a guide, not a deadline

Full-term pregnancies fall between 39 and 41 weeks, but healthy births can occur anywhere from 37 to 42 weeks. Babies born at 37–39 weeks are considered early term, those at 39–41 weeks are full term, and those at 41–42 weeks are late term. Births before 37 weeks are classified as preterm, while those after 42 weeks are postterm.

These distinctions help healthcare providers make decisions. For example, preterm babies (especially before 34 weeks) may face health challenges due to incomplete development, prompting doctors to delay labor if possible. Conversely, pregnancies continuing past 42 weeks can pose risks, as the placenta may become less efficient at delivering oxygen and nutrients, leading some providers to recommend inducing labor.