16 weeks pregnant
This calculator finds an estimated due date and how far along you are. The worked example is a pregnancy at exactly 16 weeks.
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. Here 16 weeks times 7 is 112 days.
Worked example
Start at 21 April. Count 280 days ahead to reach 26 January. Count 112 days ahead to reach 11 August. 112 divided by 7 is 16 weeks. 168 days remain. A leap year shifts dates after February by one day.
Common questions
Which trimester is week 16?
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 16 is week 3 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 14, which is 98 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 26 January, and 168 days remain from week 16.
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 26 January to 2 February.
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 21 April does not cross February. A leap year changes nothing for 26 January.