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Due date

Due date

A due date is an estimate of when a pregnant woman will have her baby. It is calculated by taking the first day of her last menstrual period (LMP), adding 7 days, and then counting backward 3 months; or by adding 40 weeks from the first day of the last menstrual period (for women with regular 28-day cycles).

For example, using the first method, if a pregnant woman's last period started on March 20, add 7 days to get March 27 and then subtract 3 months to get a due date of December 27. Using the second method, 40 weeks counted from March 20 is December 25.

Ultrasound is often used to estimate a due date based on the size of the fetus.

The due date is only an estimate of when a woman will deliver. Most women do not give birth on their due date, but they do within 2 weeks before or after.

Current as of: April 30, 2024

Author: Ignite Healthwise, LLC Staff

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This information does not replace the advice of a doctor. Ignite Healthwise, LLC, disclaims any warranty or liability for your use of this information. Your use of this information means that you agree to the Terms of Use. Learn how we develop our content.