Pregnancy Due Date Calculator

A pregnancy due date is an estimate of when a baby will be born, calculated from the first day of your last menstrual period. The standard method is Naegele's rule: add 280 days, or 40 weeks, to that date. It assumes a 28-day cycle with ovulation on day 14, which is why this calculator adjusts the result if your cycle is longer or shorter — a 32-day cycle pushes ovulation and the due date about four days later.

Only about four percent of babies arrive exactly on their due date. Roughly eighty percent are born within two weeks either side of it, and the date itself is best thought of as the centre of a window rather than an appointment. Doctors use it as a reference point for scheduling scans and tests, and for deciding when a pregnancy has passed the point at which closer monitoring is sensible. A dating ultrasound in the first trimester is more accurate than any formula, so if you have one, that date takes precedence.

Two conventions for dating are worth understanding, because they explain a common confusion. Gestational age is counted from the last period, so you are technically already "two weeks pregnant" at conception. Fetal age is counted from conception and is therefore about two weeks less. When a clinician says you are ten weeks along, they almost always mean gestational age. The calculator here uses the same convention, which is why a positive test at four weeks of gestational age corresponds to about two weeks of actual development.

This tool provides general information only and is not medical advice. Every pregnancy is different, dates can shift after a scan, and decisions about your care should always be made with your doctor or midwife.

This calculator returns estimates for general information only. It is not medical advice, diagnosis or treatment, and it cannot replace an assessment by a qualified health professional. Individual results vary, and figures such as calorie needs, body-fat percentage and heart-rate zones are approximations based on population averages rather than measurements of you.