37 weeks pregnant
Enter the first day of your last period to get a due date and the current week. The example here follows a person who is at week 37.
How it works
The due date is 280 days after the first day of your last period. Weeks of pregnancy are the days since that first day divided by 7. At 259 days along, 21 days remain.
Worked example
Take a last period that began on 28 January. Add 280 days to get a due date of 4 November. Add 259 days to reach 14 October, the start of week 37. 259 divided by 7 is 37. That leaves 21 days to go. Dates in this example use a year with 365 days.
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 4 November to 11 November.
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 28 January includes a 29 February, 4 November reads one day earlier, as 3 November.
How many months is 37 weeks pregnant?
About 8.5 months. A pregnancy is 40 weeks, a little over 9 calendar months. Months are only a rough guide. At 37 weeks there are 21 days to the due date.
Which trimester is week 37?
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 37 is week 10 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 35, which is 245 days.