How the due date estimate works
Using the same inputs as our period calculator, we add 280 days to the first day of your last period, adjusted for your average cycle length, to estimate your due date. This mirrors the method many healthcare providers use at an initial visit, before an ultrasound provides a more precise estimate.
Next steps if you think you're pregnant
If your period is late and you suspect pregnancy, a home pregnancy test followed by confirmation with a healthcare provider is the recommended next step. They can confirm timing with an early ultrasound.
Frequently asked questions
How is my due date calculated?+
The standard method (Naegele's rule) adds 280 days (40 weeks) to the first day of your last period. We also adjust slightly for cycle lengths that differ from the 28-day average.
Is this due date exact?+
No — it's an estimate. Only about 1 in 20 babies arrive on their exact due date. A healthcare provider can refine the estimate using an ultrasound.
What if my periods are irregular?+
Irregular cycles make due-date estimates less precise, since ovulation timing varies more. An early ultrasound dating scan is the most reliable way to confirm your due date in that case.