The most common way to calculate your due date is to start with the first day of your last menstrual period (LMP). Add 7 days, and then count backward 3 months. For example, if your last period started on March 20, you would add 7 days to get March 27. Then subtract 3 months to get a due date of December 27.

How do doctors determine the due date of a baby?

A typical pregnancy lasts, on average, 280 days, or 40 weeks—starting with the first day of the last normal menstrual period as day 1 .Calculating a Due DateFirst, determine the first day of your last menstrual period.Next, count back 3 calendar months from that date.Lastly, add 1 year and 7 days to that date.

How do you predict what day your baby will be born?

So without knowing the day of conception, how does anyone determine a due date? The most common way to calculate your pregnancy due date is by counting 40 weeks from the first day of your last menstrual period (LMP). And thats how most healthcare providers do it.

Is your due date at the beginning or end of 40 weeks?

Pregnancy usually lasts about 40 weeks (280 days) from the first day of your last menstrual period (also called LMP) to your due date. Your due date is the date that your provider thinks you will have your baby.