Learning when your baby is due is one of the most exciting moments of pregnancy. While a pregnancy due date calculator or ultrasound exam can be used to determine your estimated due date, if neither of those are readily available, you can use Nagele’s rule to calculate when your baby is due. Using the rule developed in the 1850s by Dr. Nagele, you can accurately calculate pregnancy due date.
How to Calculate Pregnancy Due Date
Remember when you had your last period. Make note of the first day of your last menstrual period, or LMP. If your last menstrual period started on January 7, that is the date of your last menstrual period.
Add seven days to the first day of your last menstrual period, LMP + 7. Adding seven days to the first day of a last menstrual period of January 7 brings you to January 14.
Subtract three months (LMP + 7 days — 3 months). Subtracting three months from January 14 gives you an estimated due date of October 14.