39 weeks pregnant
Pregnancy weeks are counted from the start of the last period, not from conception. See how week 39 fits the calendar in the example under the form.
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. Week 39 runs from day 273 to day 279 of the 280.
Worked example
Start at 6 March. Count 280 days ahead to reach 11 December. Count 273 days ahead to reach 4 December. 273 divided by 7 is 39 weeks. 7 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 11 December to 18 December.
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 6 March does not cross February. A leap year changes nothing for 11 December.
How many months is 39 weeks pregnant?
About 9.0 months. A pregnancy is 40 weeks, a little over 9 calendar months. Months are only a rough guide. At 39 weeks there are 7 days to the due date.
Which trimester is week 39?
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 39 is week 12 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 37, which is 259 days.