# So what is the human gestation period?

**URL:** <https://boards.straightdope.com/t/so-what-is-the-human-gestation-period/134366>\
**Category:** Factual Questions\
**Created:** [October 29, 2002, 5:50am UTC](https://boards.straightdope.com/t/so-what-is-the-human-gestation-period/134366 "2002-10-29T05:50:47Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![Cisco](https://avatars.discourse-cdn.com/v4/letter/c/ccd318/32.png) [@Cisco](https://boards.straightdope.com/u/Cisco)\
**Post date:** [October 29, 2002, 5:50am UTC](https://boards.straightdope.com/t/so-what-is-the-human-gestation-period/134366/1 "2002-10-29T05:50:47Z")

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Yesterday my sister mentioned in conversation that she learned in “Parenting” class that the actual gestation period for human females is 10 months, but they just say it’s 9 because they don’t count the first month. WTF? That’s like saying “there’s really 25 cigarettes in a pack but they just say 20 because the first 5 don’t count.” I just find it hard to believe that I’ve heard 9 months all my life but it’s really just a conspiracy to oust the first month. So what’s the dope here? 9 or 10 months?  
(I realize it isn’t _exactly_ 9 _or_ 10 months, but gimme a rough average.)

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**Author:** ![InternetLegend](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/internetlegend/32/13154_2.png) [@InternetLegend](https://boards.straightdope.com/u/InternetLegend)\
**Post date:** [October 29, 2002, 6:18am UTC](https://boards.straightdope.com/t/so-what-is-the-human-gestation-period/134366/2 "2002-10-29T06:18:03Z")

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It’s 40 weeks.

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**Author:** ![don\_t\_ask](https://avatars.discourse-cdn.com/v4/letter/d/e68b1a/32.png) [@don\_t\_ask](https://boards.straightdope.com/u/don_t_ask)\
**Post date:** [October 29, 2002, 6:21am UTC](https://boards.straightdope.com/t/so-what-is-the-human-gestation-period/134366/3 "2002-10-29T06:21:08Z")

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What makes it tricky is that the expected delivery date is 38 weeks after fertilization, but the length of pregnancy is commonly given from the start of woman’s last menses (LMP) thus giving a pregnancy of 40 weeks.

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**Author:** ![don\_t\_ask](https://avatars.discourse-cdn.com/v4/letter/d/e68b1a/32.png) [@don\_t\_ask](https://boards.straightdope.com/u/don_t_ask)\
**Post date:** [October 29, 2002, 6:25am UTC](https://boards.straightdope.com/t/so-what-is-the-human-gestation-period/134366/4 "2002-10-29T06:25:17Z")

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[Here](http://transitiontoparenthood.com/ttp/birthed/duedates.htm) is how to work out due dates. Also provides different estimates for lenths of gestation.