What is a pregnancy wheel?
A pregnancy wheel — also called an OB wheel, gestation wheel or maternity wheel — is a pair of cardboard discs used by midwives and doctors. You line up the first day of the last menstrual period on the outer disc and read off the estimated due date and the current week of pregnancy. It is a quick visual version of Naegele’s rule.
Why use an online pregnancy wheel?
Paper wheels are handy but can be a few days out, because they are printed for a non-leap year and the scales are small. This online pregnancy wheel calculates the exact dates and then draws the familiar wheel: 40 segments, one per week, coloured by trimester, with your current week highlighted and your due date in the centre. You can start from your last period, your due date or an ultrasound result.
Reading the wheel
- Pink segments: first trimester (weeks 1–13).
- Purple segments: second trimester (weeks 14–27).
- Blue segments: third trimester (weeks 28–40).
- Highlighted segment: the week you are in now; solid segments are weeks already completed.
The wheel works from any of the three starting points, and you can print or share the result like any other calculator on this site. For the numbers behind the wheel, see the Naegele’s Rule Calculator and the EDD Calculator.