31 weeks pregnant
Pregnancy weeks are counted from the start of the last period, not from conception. See how week 31 fits the calendar in the example under the form.
How it works
Due date equals the first day of your last period plus 280 days. Weeks along equals days since that first day divided by 7, rounded down. On this page the pregnancy is 217 days from the first day of the last period.
Worked example
Use 10 July as the first day. Add 280 days for a due date of 16 April. Week 31 starts 217 days in, on 12 February. 217 divided by 7 is 31. Subtract 217 from 280 to get 63 days to go. This example assumes a 365-day year.
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 16 April to 23 April.
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. If the span from 10 July includes a 29 February, 16 April reads one day earlier, as 15 April.
How many months is 31 weeks pregnant?
About 7.1 months. A pregnancy is 40 weeks, a little over 9 calendar months. Months are only a rough guide. At 31 weeks there are 63 days to the due date.
Which trimester is week 31?
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 31 is week 4 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 29, which is 203 days.