How long does pregnancy last?

Pregnancy is counted from the first day of your last menstrual period. This means an extra 2 weeks are counted at the beginning of your pregnancy when you aren’t actually pregnant. So pregnancy lasts 10 months (40 weeks)—not 9 months—because of these extra weeks.

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This information is designed as an educational aid for the public. It offers current information and opinions related to women's health. It is not intended as a statement of the standard of care. It does not explain all of the proper treatments or methods of care. It is not a substitute for the advice of a physician. Read ACOG’s complete disclaimer.