Health & Fitness Calculators
Due Date Calculator
Estimate a baby’s due date from the last menstrual period or the conception date using Naegele’s rule.
Quick guide
Choose whether you know the last menstrual period or the conception date, then enter that date. Naegele’s rule adds 280 days to the period date (or 266 days to conception) to estimate the due date and the time remaining.
Read the full explanationHow It Works
Naegele’s rule adds 280 days to the first day of the last period. If the conception date is known instead, adding 266 days gives the same estimate.
Formula Used
Due date = LMP + 280 days = conception + 266 days.
Example Calculation
A last period starting March 1 gives an estimated due date around December 6.
Practical Use Cases
- Get a quick due-date estimate.
- Cross-check dates from an ultrasound.
- Plan maternity leave and key milestones.