Calculating a Due Date

Calculating a Due Date

A typical pregnancy lasts, on average,
280 days, or 40 weeks—starting with the first day of the last normal menstrual period
day 1. An estimated due date can be calculated by following steps 1 through 3:

  1. First, determine the first day
    of your last menstrual period.

  2. Next, count back 3 calendar
    months from that date.

  3. Lastly, add 1 year and 7 days to
    that date.

Due Date Calendar

For example: Your last menstrual
period began on September 9, 2020. Counting back 3 calendar months would be June 9,
Adding 1 year and 7 days would bring you to June 16, 2021, as your estimated due date.

This 3-step method is referred to as
Naegele’s Rule and is based on a normal 28-day menstrual cycle. Therefore, dates may
to be adjusted for longer or shorter menstrual cycles. 

You may also estimate your delivery
date by using steps 1 and 2 below and the chart:

  1. First, locate the first day of
    your last menstrual period (in black text).

  2. Next, note the date directly
    below. This is your estimated date of delivery (in blue text).