Calculate your estimated due date from LMP or conception date.
Choose whether to calculate from the last menstrual period or conception date, enter that date, then review the estimated due date and pregnancy timeline.
Only a small proportion of babies arrive on the estimated due date; it is a reference point rather than a promise.
Pregnancy is conventionally dated from the first day of the last menstrual period, with an estimated due date about 40 weeks later. If a conception date is known, the calculator can use that instead. Either method gives a planning date rather than a prediction of the exact day labour will begin.
An LMP estimate works best when the period date is known and cycles are reasonably regular. Pregnancy, Birth and Baby notes that ultrasound can also be used to estimate gestational age and that most babies are born across a range of weeks, not on one exact date. See Working out your due date. Use the result for calendars and appointment planning, and use the due date recorded by your maternity care team for clinical decisions.