You can use the first day of a your last menstrual period (LMP) to calculate your due date.
How So? To figure out your due date, count forward 40 weeks (or 280 days) from the first day of your last period.
Why 40 Weeks? Because that’s the length of the average pregnancy.
Not a Fan of Math? No Worries! Try a Pregnancy Due Date Calculator instead.
Common Question: Why Do Women Use the First Day of Their LMP as the Pregnancy Starting Point Rather Than the Day of Conception (i.e. When the Egg and Sperm Meet)?
Because most women know the first day of their LMP but are hazy about when fertilization occurred.
The Bottom Line
Use the first day of your last menstrual period to determine your due date. If you’re not sure when that was, don’t worry, your doctor can do an early ultrasound to estimate when you’ll deliver.
