Calculate your due date and week of pregnancy

From the first day of your last period, from an ultrasound measurement or from the day of conception: this calculator gives the estimated due date, today’s week of pregnancy and the dates that follow from it – from the end of the first trimester to the start of maternity leave in Austria.

What do you know?
Naegele’s rule assumes 28 days.

Why 40 weeks – and why you were never pregnant for all of them

Pregnancy is counted from the first day of your last period, not from conception. That day is about two weeks before the egg was even released. So in week five you have been pregnant for roughly three weeks – and at the due date, the child is 38 weeks old, not 40.

This seemingly awkward way of counting has a good reason: the first day of bleeding is an event you noticed. The day of ovulation is not.

Which method is the most accurate

The ultrasound measurement in the first trimester, by a wide margin: between 7+0 and 13+6 weeks the crown-rump length dates the pregnancy to within about five days. That is why a due date determined this way is not corrected later – not even if a later scan shows a larger or smaller child. From the second trimester on, children vary so much in size that a measurement says more about the child than about the date.

Sources

  1. Robinson HP, Fleming JEE: A critical evaluation of sonar crown-rump length measurements. British Journal of Obstetrics and Gynaecology 82 (1975) 702–710
  2. Sozialministerium: Eltern-Kind-Pass
  3. Mutterschutzgesetz (MSchG), § 3: Beschäftigungsverbote für werdende Mütter
What this tool cannot do

It works with averages. Your body does not. The result is a starting point for a conversation, not a finding – and it cannot see what an examination would show.

Questions about your result? Arrange an appointment.