Due Date Calculator
Free due date calculator: enter the first day of your last period to estimate your baby's due date, conception date and how many weeks pregnant you are now.
About this tool
A positive test brings one immediate question: when is the baby coming? Doctors answer it with Naegele's rule - add 280 days (40 weeks) to the first day of your last menstrual period. A due date calculator applies that rule instantly and also estimates the conception date and your current week of pregnancy.
Only about 1 in 20 babies arrives exactly on the due date; think of it as the centre of a four-week window, not an appointment. Still, the date anchors everything: prenatal checkups, the anatomy scan around week 20, maternity leave planning, and - eventually - the nursery.
How to use
Pick the first day of your last menstrual period on the date picker, enter your average cycle length (28 if you are not sure), and press Calculate Due Date.
You get the estimated due date, the approximate conception date (about two weeks after the period started), and roughly how many weeks pregnant you are today. If your cycles are much longer or shorter than 28 days, the tool adjusts the due date accordingly.
The math behind it
Naegele's rule: due date = LMP + 280 days, adjusted by (cycle length - 28). Conception is estimated at LMP + 14 days, the typical ovulation point in a 28-day cycle.
The 40 weeks are counted from the last period - not from conception - which is why you are considered 'two weeks pregnant' at the moment of conception. Ultrasound dating in the first trimester can refine the estimate by a few days.
Frequently asked questions
How accurate is a due date calculator?
Why is pregnancy counted from the last period, not conception?
My cycles are irregular - can I still use this?
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