10 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 10.
How it works
Add 280 days to the first day of your last period to get the due date. To find the current week, count the days since that day and divide by 7. Week 10 runs from day 70 to day 76 of the 280.
Worked example
Say the first day of the last period is 3 October. The due date is 280 days later, on 10 July. After 70 days the date is 12 December. 70 divided by 7 is 10. That is the start of week 10. The 210 days left run to the due date. This example uses a 365-day year.
Common questions
Which trimester is week 10?
First 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 10 is week 10 of the first 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 8, which is 56 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 10 July, and 210 days remain from week 10.
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 10 July to 17 July.
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 3 October includes a 29 February, 10 July reads one day earlier, as 9 July.