Due Date Calculator

Due Date Calculator

A due date, also known as the estimated date of confinement (EDC), represents the approximate day a baby is expected to be born. While it is often shown as a single date, it is more accurate to think of it as a time range.

Last Menstrual Period (LMP)

The most common method for estimating a due date is based on the first day of the last menstrual period. This approach assumes an average pregnancy length of 280 days, or 40 weeks.

Gestational age is calculated from LMP regardless of whether pregnancy is defined as beginning at fertilization or implantation. Most full-term pregnancies last between 37 and 42 weeks.

Ultrasound Dating

Ultrasound dating estimates gestational age by comparing fetal size to established growth standards. Early ultrasounds are especially accurate and are commonly used to confirm or adjust due dates.

The procedure is non-invasive, has no known risk to the baby, and is a standard part of prenatal care.

Conception Date Method

If the conception date is known, a due date can be estimated by adding approximately 38 weeks from that date. This method typically results in a due date about two weeks later than LMP-based calculations.

In Vitro Fertilization (IVF)

Due date estimation for IVF pregnancies is often more precise, since the exact embryo transfer date is known. Calculations may be based on egg retrieval, fertilization timing, or the date of a 3-day or 5-day embryo transfer.

This calculator uses the embryo transfer date to estimate the due date.

Due Date as a Medical Reference

Babies born between 37 and 42 weeks are generally considered term. These weeks are further categorized to help guide medical decisions.

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

Babies born before 37 weeks are considered preterm, while those born after 42 weeks are post-term. These ranges help doctors decide whether monitoring, intervention, or induction is necessary.