Pregnancy Due Date Calculator
Estimate an approximate pregnancy due date and current gestational week from the first day of your last menstrual period.
Your results
This is a general estimate using Naegele's rule; your healthcare provider may adjust this using an ultrasound scan.
Calculation breakdown
- Naegele's rule
- Due date = first day of last menstrual period + 280 days
Worked example
If the last menstrual period began on 1 January, the estimated due date is 8 October, 280 days later.
Assumptions
- Assumes a typical 28-day menstrual cycle with ovulation around day 14.
- An early ultrasound scan can provide a more accurate estimate for irregular cycles.
How this calculator works
This calculator estimates an approximate pregnancy due date using Naegele's rule, which adds 280 days (40 weeks) to the first day of your last menstrual period, and also shows your current estimated gestational week. This is a general estimate; your healthcare provider may adjust the date using an ultrasound scan.
Frequently asked questions
How is the due date calculated?
This calculator uses Naegele's rule, adding 280 days to the first day of your last menstrual period, assuming a standard 28-day cycle.
What if my cycle isn't 28 days?
This estimate assumes a typical cycle length; irregular cycles can shift the actual due date, so an early ultrasound is often more accurate.
Is this the exact day my baby will be born?
No, only a small percentage of babies arrive exactly on their estimated due date; it is a guide for planning purposes.
Results are estimates only and are not financial, tax, legal or credit advice.