What a pregnancy wheel does
For decades, the pregnancy wheel — also called an obstetric wheel, OB wheel, gestation wheel or maternity wheel — has sat on desks in clinics. It is two cardboard discs: one marked with calendar dates and one with weeks of pregnancy. Turn the inner disc so that week 0 lines up with the first day of the last period, and the wheel shows the due date at 40 weeks and the week of pregnancy for any date in between.
This online Pregnancy Wheel does the same with your own dates. All 40 weeks run clockwise from the top, coloured by trimester. The months of your pregnancy sit around the outside, and a pointer marks today. The hub in the middle shows how far along you are and your due date.
How to read your wheel
- Top of the wheel: week 0 (the first day of your last period) and week 40 (your due date) meet here.
- Numbers inside the ring: weeks 0, 4, 8 and so on — every fourth week is labelled.
- Coloured band: pink for the first trimester (to 13 weeks 6 days), lavender for the second (14 to 27 weeks 6 days), mint for the third (28 weeks onward).
- Outer labels: where each calendar month begins in your pregnancy.
- Pointer: today’s position.
Paper wheel vs online wheel
| Paper wheel | Online wheel | |
|---|---|---|
| Precision | Can be a day or two out | Exact days, leap years included |
| Cycle length | Assumes 28 days | Adjustable in the calculator |
| Today’s position | You find it by hand | Marked automatically |
| Key dates | Read one at a time | Listed underneath |
Other ways to see your pregnancy
Prefer a calendar? The Pregnancy Calendar by Due Date lays the same weeks out month by month. For a week-by-week list with what typically happens in each week, see the Pregnancy Timeline.