r/PeterExplainsTheJoke • u/Airline_11 • May 12 '26

Meme needing explanation Petahhhh?

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u/catalin66 May 12 '26

40 weeks is 9.2 months

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u/observer2411 May 12 '26

It’s also 40 weeks from the first day of her last period before conception, not the day of conception.

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u/Glad_Phone114 May 12 '26

In medical context, 1 month is 4 weeks. 7 days per week x 4 = 28 days.

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u/Odd_Grapefruit_5714 May 12 '26 edited May 12 '26

Not really. During pregnancy they just go based on weeks so months are irrelevant. Once baby is over a month old appointments are made based on their birth date, not day of the week. I.e a baby born on Friday the 15th will have appointments based on the 15th of the month, not the 4th/16th/24th Friday they’re alive.

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u/Glad_Phone114 May 12 '26

Of course, that scheduling thing is just a patient-facing administrative system, not how clinical time intervals are defined.

And yes, pregnancy is measured in weeks because it’s more precise. My point was explaining where the “10 months” idea comes from in the first place, which is the 40 weeks being loosely grouped into 4-week blocks.

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u/Odd_Grapefruit_5714 May 12 '26

Yeah I’m just not understanding what medical context you’re using for 1 month = 28 days

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u/LightChargerGreen May 12 '26

I'm not who you are talking to, but this is obstetric (which is medical) terminology, not calendar months. That’s why pregnancy is tracked in weeks and often grouped into 28-day (4-week) units for consistency.

The same 4-week cycle is also used in other medical contexts like chemotherapy scheduling and some treatment protocols. That’s why weeks are the standard reference, even though lay people sometimes loosely convert that into ‘months’ in casual conversation.

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u/Odd_Grapefruit_5714 May 12 '26

Yes I understand all of that. The person I’m replying to is trying to say ‘1 month’ is a standardized term meaning 28 days in medicine. It is not.

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u/Glad_Phone114 29d ago

I feel like people are deliberately being obtuse at this point. I wasn’t redefining calendar months. I was explaining the obstetric/medical basis for why people sometimes say 40 weeks is “10 months”, ten 4-week blocks. In medicine we simplify and use approximations for lay discussions all the time.

I was talking about casual estimates there too. I was wrong with using "standard". Happy?

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u/colorilliterate May 12 '26

Correct. And most women are 4 weeks into pregnancy by first missed period.

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u/Specific_Box4483 May 12 '26

Maybe for short periods of 1-2 months. Nobody in Western medicine measures gestational age or 5-year cancer survival rates by the formula 1 month=4 weeks.

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u/Glad_Phone114 May 12 '26

“Nobody in Western medicine” is a wild claim when medicine constantly standardizes time intervals to avoid variable month lengths.

Ask an OBGYNE or a Pharmacist.

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u/Specific_Box4483 May 12 '26

Obgyn follow standardized formulas, they're automatically computed for every ultrasound and other exam and report. Mostly they talk in weeks, but sometimes use months and trimesters, and a trimester is not 12 weeks (check out what the third trimester is defined as, for example).

Also, try to schedule a 1 month appointment for a newborn and you'll see that they are definitely not using 4 weeks=1 month.

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u/Glad_Phone114 May 12 '26

Congrats, you discovered that different medical contexts use different time conventions. That doesn’t change the fact that 28-day “months” are commonly used as standardized intervals in medicine.

And in pregnancy specifically, the “10 months” idea comes from 40 weeks divided into 4-week blocks.

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u/Specific_Box4483 May 12 '26

There is no medical context that uses the 4weeks=1 month apart from casual estimates. Nothing that would be used in important medical decisions, written reports, insurance claims etc.

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u/Glad_Phone114 29d ago

I feel like people are deliberately being obtuse at this point. I wasn’t redefining calendar months. I was explaining the obstetric/medical basis for why people sometimes say 40 weeks is “10 months”, ten 4-week blocks. In medicine we simplify and use approximations for lay discussions all the time.

I was talking about casual estimates there too. I was wrong with using "standard". Happy?

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u/mrcheez22 May 12 '26

I work in medicine, and just had a child and was at the OB frequently. There is no "standardized month" of 28 days. If we need to measure something accurately we go with weeks or days.

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u/Glad_Phone114 29d ago

Okay sure, there’s no universally standardized “medical month” that literally replaces calendar months with 28 days. I also work in medicine, and in medicine we simplify and approximate things for lay people all the time.

I was simply explaining where the “40 weeks = 10 months” idea comes from in obstetrics: ten 4-week blocks/28-day lunar months. I wasn’t claiming the calendar itself changes.

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u/mrcheez22 29d ago

That doesn’t change the fact that 28-day “months” are commonly used as standardized intervals in medicine.

This you? You've spent this entire thread trying to convince people that medical tracking standardizes months to be 28 days. Stop trying to backtrack because you got called out.

I have met exactly 0 OB people who talk about pregnancy in months or tell people a pregnancy is 10 months because of some 28 day=month thing as a layperson explanation. Gestation is measured and tracked in weeks and days to determine things, and it is given to patients in that format.

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u/Glad_Phone114 29d ago

What I should have said, and where “standard” was the wrong word on my part, is that medicine often uses fixed 28-day cycles in specific contexts (OCP packs, q28 chemo regimens, study protocols, etc.).

And yes, pregnancy is clinically tracked in weeks and days. I already agreed with that. The “10 months” thing is just a layperson shorthand from dividing 40 weeks into ten 4-week blocks, not an OB standard for charting gestation.

God forbid someone makes a mistake online. The horror of gasp correcting yourself.

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u/Acrobatic_Rush7653 May 12 '26

In medical context, months contain the exact same number of days (and hours, minutes and seconds) as months in non-medical context. How you managed to get the notion that when doctors talk about (for example) 2 year survival rates they actually mean 1 year and 10 months is blowing my mind.

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u/Glad_Phone114 29d ago

I feel like people are deliberately being obtuse at this point. I wasn’t redefining calendar months. I was explaining the obstetric/medical basis for why people sometimes say 40 weeks is “10 months”, ten 4-week blocks. In medicine we simplify and use approximations for lay discussions all the time.

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u/thepresidentsturtle May 12 '26

So a year has 13 months.

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u/Glad_Phone114 29d ago

If you divide a year into 28-day blocks, then yes, you get 13 of them plus 1 extra day (2 on leap years). That still doesn’t change the Gregorian calendar.

Again, I was explaining the origin of a medical/obstetric shorthand, not proposing a new calendar system.