Pregnancy Due Date Calculator

Related pregnancy tools: Due date · Pregnancy weeks · Trimester dates · IVF due date · Ovulation estimate · Conception estimate

This is an estimated due date, not a prediction of the day of birth. Follow the date assigned by your healthcare provider.

About this calculator

An estimated due date is calculated at 280 days, or 40 weeks, measured from the first day of the last menstrual period. Working a due date out this way is known as Naegele's rule. The last-period method assumes ovulation about 14 days before the next period, so this calculator adjusts the estimate when a different cycle length is entered. The conception method counts 266 days from conception. The IVF method counts from the transfer date, using 261 days for a day-5 blastocyst transfer and 263 days for a day-3 transfer. For pregnancies not dated by IVF, an early ultrasound can establish or confirm dating. For IVF, use the embryo age and transfer date and follow your clinic's assigned due date.

This is an estimate and not medical advice. Actual birth may occur before or after the estimated due date. Dating scans, the health of the pregnancy and many other factors can change the picture, so any estimate here should be confirmed with a midwife or doctor. For background on how pregnancy is dated, the American College of Obstetricians and Gynecologists explains the standard methods.

Sources checked 9 October 2026. These methods were checked against published guidance; this tool has not been clinically reviewed.

Frequently asked questions

How is a due date calculated?

The most common method counts 280 days, which is 40 weeks, from the first day of the last menstrual period. This is called Naegele's rule. It assumes ovulation around two weeks into the cycle, so this calculator adjusts the result if the cycle is shorter or longer than 28 days. The conception, IVF transfer and ultrasound methods count from a different starting point but aim at the same estimated 40-week due date.

How accurate is an estimated due date?

A due date is an estimate, not a fixed appointment. Actual birth can occur before or after it. For pregnancies not dated by IVF, early ultrasound can help establish dating. For IVF, embryo age and transfer date determine the estimated due date. Follow your healthcare provider's assigned date. Full term is 39 weeks through 40 weeks and 6 days.

What is the difference between the last-period and conception methods?

Pregnancy is normally dated from the first day of the last menstrual period, which is about two weeks before conception actually happens. That is why the last-period method uses 280 days and the conception method uses 266. If you have an estimated conception date, the conception route can provide a calendar estimate. Ovulation tracking does not establish the exact moment of fertilisation. If you only know the last period, use that method and enter the usual cycle length.

How does an IVF transfer date change the calculation?

With IVF, embryo age and transfer date provide the dating inputs. The embryo's age at transfer matters. A day-5 transfer uses a blastocyst, so the due date is 261 days after the transfer. A day-3 transfer is two days earlier in embryo development, so it is 263 days after the transfer. Choose the embryo age supplied by your fertility clinic.

Is this calculator medical advice?

No. This tool gives a general estimate using standard dating methods, and it is not a substitute for professional care. A due date should be confirmed by a midwife or doctor, usually with a dating ultrasound. If you have any questions about a pregnancy or about your dates, speak to a qualified healthcare provider.

Last updated 2026-10-17