Expected Delivery Date
When anticipating a baby's arrival, do not rely solely on the expected delivery date, as the baby will not necessarily be born on this date. The baby could be born up to 15 days earlier or later than the expected date and still be considered a regular delivery. The length of pregnancy, or how long the baby is inside the mother, is not fixed. Generally, the term of pregnancy begins on the last day of menstruation and ends 280 days later (28 days = 1 month, 10 months = 40 weeks).
Calculating the expected delivery date
# Month of delivery: Nine is added when the last menstruation was between January and March, and three is subtracted if it was between April and December.
# Day of delivery: Seven is added to the first day of the last period to calculate the expected delivery date.
# Example: o If Feb. 9 was the day of last period, 2 + 9 = 11 (the month), 9 + 7 = 16 (the day). The expected delivery date is Nov. 16.
o If Sept. 25 was the day of last period, 9 - 3 = 6 (the month), 25 + 7 = 32 (the day). The expected delivery date is July 2.