23 weeks pregnant
Pregnancy weeks are counted from the start of the last period, not from conception. See how week 23 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. Here 23 weeks times 7 is 161 days.
Worked example
Use 14 November as the first day. Add 280 days for a due date of 21 August. Week 23 starts 161 days in, on 24 April. 161 divided by 7 is 23. Subtract 161 from 280 to get 119 days to go. This example assumes a 365-day year.
Common questions
Which trimester is week 23?
Second 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 23 is week 10 of the second 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 21, which is 147 days.
How accurate is a due date?
Only a small share of babies arrive on the due date. Most arrive within a couple of weeks either side. Treat the date as the middle of a window. Here the due date is 21 August, and 119 days remain from week 23.
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 21 August to 28 August.
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 14 November includes a 29 February, 21 August reads one day earlier, as 20 August.