Pregnancy Due Date Calculator
Due date, weeks pregnant and trimester.
Key dates
This is an estimate for information only, not medical advice. Only about 1 in 25 babies arrive on the due date. Your doctor or midwife may set a different date from an ultrasound scan.
About this tool
Pregnancy Due Date Calculator estimates when your baby is due using the first day of your last menstrual period (adjusted for your cycle length) or a known conception date. It also shows how far along you are today, the trimester and dates for common milestones. It is an estimate for planning, not medical advice.
How to use Pregnancy Due Date Calculator
- Choose last period or conception date.
- Enter the date and your usual cycle length.
- Read your due date, current week and milestones.
Questions people ask
How is the due date calculated?
It uses Naegele's rule: due date = first day of last period + 280 days (40 weeks). For cycles longer or shorter than 28 days, the date moves by the difference. From a conception date, the due date is conception + 266 days.
Why is pregnancy counted from the last period?
Most people do not know the exact day they conceived, but they do know when their last period started. Counting from that day adds about 2 weeks before conception, which is why a pregnancy is said to last 40 weeks.
How likely is birth on the due date?
Only about 4% of babies are born on their due date. Most arrive between 37 and 42 weeks. An early ultrasound scan, usually at 8 to 14 weeks, gives the most accurate date and your care provider may change it.