15 weeks pregnant
Doctors count pregnancy from the first day of the last period. This page shows what week 15 looks like in dates and lets you work out your own due date.
How it works
Start on the first day of your last period. Move ahead 280 days for the due date. Divide the days that have passed by 7 to get weeks. The remainder is extra days. Week 15 runs from day 105 to day 111 of the 280.
Worked example
Use 18 March as the first day. Add 280 days for a due date of 23 December. Week 15 starts 105 days in, on 1 July. 105 divided by 7 is 15. Subtract 105 from 280 to get 175 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 23 December to 30 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 18 March does not cross February. A leap year changes nothing for 23 December.
How many months is 15 weeks pregnant?
About 3.5 months. A pregnancy is 40 weeks, a little over 9 calendar months. Months are only a rough guide. At 15 weeks there are 175 days to the due date.
Which trimester is week 15?
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 15 is week 2 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 13, which is 91 days.