Due date by last period
Enter the first day of your last period to get an estimated due date and the current week of your pregnancy. The estimate assumes a cycle of about 28 days with ovulation near day 14.
How it works
Add 280 days to the first day of the last period. That is 40 weeks. The current week is the days since that first day divided by 7.
Worked example
Say the first day of the last period is 22 June. Add 280 days to reach 29 March. Add 140 days to reach 9 November, which is the start of week 20. 140 divided by 7 is 20. This example uses a 365-day year.
Common questions
What if I do not remember the date?
Use your best estimate, or ask your doctor for ultrasound dating. A guess that is 7 days late moves 29 March to 5 April.
What if my cycles are longer than 28 days?
Ovulation then comes later. The due date can move later by the extra days. With a 35-day cycle from 22 June, the due date would move 7 days to 5 April.
Is the first day the first day of bleeding?
Yes. Count from the first day of full flow and not from spotting. If bleeding began on 22 June, the 280 days end on 29 March.
Which day starts week 1?
Week 1 starts on the first day of the last period. You are counted as pregnant before conception. From 22 June, week 5 starts on 20 July.