40 weeks pregnant
Week 40 of pregnancy means 280 days since the last period began. Use the form to place your own dates, or read the example below.
How it works
Forty weeks is 280 days. Add 280 days to the first day of your last period for the due date. Divide the days that have passed by 7 for weeks and days. On this page the pregnancy is 280 days from the first day of the last period.
Worked example
Start at 9 April. Count 280 days ahead to reach 14 January. Count 280 days ahead to reach 14 January. 280 divided by 7 is 40 weeks. 0 days remain. A leap year shifts dates after February by one day.
Common questions
What if my cycle is not 28 days?
The 280 day rule assumes ovulation near day 14. If your cycle is much longer or shorter, your doctor may adjust the due date, often with an ultrasound. With a 35-day cycle some clinicians add 7 days, which would move 14 January to 21 January.
Does a leap year change the due date?
It can. A year with an extra day in February moves dates after that day by one. The calculator above uses the real calendar for your dates. The span from 9 April does not cross February. A leap year changes nothing for 14 January.
How many months is 40 weeks pregnant?
About 9.2 months. A pregnancy is 40 weeks, a little over 9 calendar months. Months are only a rough guide. At 40 weeks there are 0 days to the due date.
Which trimester is week 40?
Third trimester. The first trimester covers weeks 1 to 13, the second covers weeks 14 to 27 and the third runs from week 28 to the birth. Week 40 is week 13 of the third trimester.
Why do weeks start from the last period and not conception?
Most people know the date of their last period but not the day of conception. Counting from the last period gives everyone the same starting point. A pregnancy is about two weeks longer on paper than from conception. Counted from conception, this would be week 38, which is 266 days.