Ori ToolsHow to use
- Enter the first day of your last period.
- Enter your usual cycle length.
- Press Calculate.
When to use it
- Early pregnancy planning
- Checking a date given by your clinic
- Sharing a rough date with family
Naegele's rule
The standard estimate adds 280 days (40 weeks) to the first day of the last period, assuming a 28-day cycle. Longer or shorter cycles move the date by the difference. Only about 1 in 20 babies arrive exactly on the due date.
Frequently asked questions
Is an ultrasound date more accurate?
Yes, an early ultrasound is usually preferred.
Why adjust for cycle length?
Ovulation happens later in longer cycles.
Is this medical advice?
No, follow your clinician's dates.