Pregnancy Due Date Calculator
Enter the first day of your last menstrual period and your usual cycle length. The calculator estimates your due date using Naegele's rule and shows how far along you are today.
Pregnancy Due Date
Due date and weeks pregnant
How it works
- Due date ≈ first day of last period + 280 days (40 weeks).
- Cycles longer or shorter than 28 days shift the date by the difference.
- Only about 1 in 20 babies arrive exactly on the due date.
- An early ultrasound gives a more accurate date — this is an estimate, not medical advice.
Worked example: last period 1 January, 28-day cycle
- 11 January + 280 days.
- 2No cycle adjustment (28 days).
Estimated due date: 8 October
Pregnancy milestones (from first day of last period)
| Milestone | Week |
|---|---|
| End of first trimester | 13 |
| End of second trimester | 27 |
| Full term | 37 |
| Due date | 40 |
Frequently asked questions
How is the due date calculated?
By adding 280 days to the first day of your last period, adjusted for cycle length. This is Naegele's rule, used by most doctors and midwives.
How accurate is the due date?
It is an estimate. Most babies are born between 38 and 42 weeks; your care provider may adjust the date after an ultrasound.
Why count from the last period and not conception?
The date of the last period is usually known, while conception is not. Pregnancy weeks include about two weeks before conception.
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