Normal pregnancy period is 40 weeks from the date of the last menstrual period.
Pregnancy due date can be calculated practically by adding 7 days to the beginning of the last period and going back 3 months. Pregnancy due date is the last date it may have been born. Most of the births do not wait until this date, it takes 38-40 weeks. Sometimes births may pass this date for 1 or 2 weeks. In other words, the birth usually occurs 1-2 weeks before the calculated date.
You can calculate your pregnancy due date manually.
Check this sample:
Estimated date of birth for someone with last menstrual date of April 10
10 + 7 = April 17
If you go back 3 months from April – January -> January 17.
Sample:
For someone whose last menstrual date is February 5:
5 + 7 = February 12
12 If you go back 3 months in February, pregnancy due date will be November 12th.
However, this method can be a cause for mistakes especially in people with menstrual irregularity . In this case, pregnancy due date is calculated by using ultrasonic measurements.
Or you can use Due Date Calculater 🙂