Due date calculator
In order to calculate your pregnancy due date, of EDD, just count from the first day of your last period. Then subtract 3 months and add 7 days to this date. Known as Naegele’s Rule, this method is based on the thought that a woman ovulates on day 14 of her cycle. Ovulation causes the body to increase slightly in temperature. For women who ovulate after day 14 of their cycle, a method which calculates using the first day of an overall thermal shift, subtracting 7 days and adding 9 months works better. This method is known as Prem’s Rule. An average pregnancy lasts about 280 days or 40 weeks. To help with the process, there are numerous online <a href=\"http://www.pregnancyweektoweek.com/calculator.html\">due date calculators</a> which merely ask for the date of your last period and do all the calculations for you. However accurate you may believe the due date to be, a large portion of babies are not born on their estimated dates. In fact, about 8-% are born within 10 days after the calculated date. This is known as a full term pregnancy which can extend to about 42 weeks. About 8-10% of babies are born before their estimated due dates. Premature babies also fall into this category, although depending on just how premature or early, the baby has varying survival potentials. Knowing the pregnancy due date is important for determining if the pregnancy is progressing smoothly and if the baby is developing correctly for each developmental stage.
Current guidance (today's medical sources): A pregnancy due date is an estimate, not a fixed deadline. The common method, Naegele's rule, counts forward forty weeks (280 days) from the first day of the last menstrual period — in practice, taking that date, subtracting three months, and adding seven days. Because it assumes a regular twenty-eight-day cycle with ovulation around day fourteen, it is only an approximation, and an early ultrasound often gives a more accurate date. Only about one in twenty babies arrives exactly on the estimated date. The calculator on this page is for general information; a healthcare provider confirms dating.
Estimate your due date
Enter the first day of your last menstrual period. This uses Naegele’s rule (+280 days) and is an estimate only — your healthcare provider confirms your dating, often with an early ultrasound.
Contact your healthcare provider promptly about heavy vaginal bleeding, severe or persistent abdominal pain, a high fever, severe or sudden headache, vision changes, or fainting. Seek urgent care if you are worried — these can be signs that need medical attention.
Sources: ACOG — Methods for Estimating the Due Date; NHS — How can I work out my due date?; Mayo Clinic — Due date calculator / Pregnancy due date. Informational only. See our sources & medical-review policy.
Follow your pregnancy week by week
A sourced guide to every week from 1 to 40.
Open the week-by-week guide →Informational only — not medical advice. Pregnancy Week to Week is a general educational reference. It is not a substitute for professional medical care, diagnosis, or treatment. Every pregnancy is different: always consult your doctor, midwife, or other qualified healthcare provider about your own pregnancy, and never disregard or delay professional advice because of something you read here. In an emergency, contact your maternity unit or local emergency number immediately.