This calculator estimates your due date and current stage of pregnancy based on the first day of your last menstrual period (LMP), the standard method used by most doctors.
Using Naegele's rule, 280 days (40 weeks) are added to the first day of your last period to estimate your due date, and your current pregnancy week is calculated from today's date.
Example: LMP on 1 January:
Due Date = 1 January + 280 days = 8 October (approximately)
It's an estimate - only around 5% of babies are born on their exact due date, though most arrive within a couple of weeks of it.
This calculation assumes a standard 28-day cycle; an ultrasound dating scan is more accurate if your cycles are irregular.
A full-term pregnancy is generally considered to be between 39 and 40 weeks.