Due date, due week, due month
A due date is a single day 40 weeks after the start of your last period — but birth happens across a window. That is why many parents find it more useful to think in wider terms:
| Term | Meaning |
|---|---|
| Due date | Exactly 40 weeks (280 days) from the first day of the last period |
| Due week | The 7 days centred on the due date — three days before to three days after |
| Due month | The calendar month of the due date |
| Birth window | 37 to 42 weeks — the usual range for birth |
This Due Calculator shows all four. Use the due date for medical dating, and the due week or birth window for planning things like leave, family visits or travel.
Why “due” is not a deadline
The 40-week figure is an average. Babies born anywhere from 37 to 41 weeks are considered term, and first babies are slightly more likely to arrive after the due date than later babies. Only a small share arrive on the date itself. Treating the due date as the middle of a window rather than an appointment helps avoid stress if it passes.
Planning around your due window
- Have your hospital bag and transport plan ready by 36–37 weeks.
- If you are arranging help at home, ask for flexibility of a couple of weeks either side.
- Avoid booking non-essential trips or commitments in the weeks around your due date.
Want the term dates spelled out? See the Pregnancy Term Calculator. To count down, use the Days Until Due Date Calculator.