# Why are 7 "cat years" equal to one people year? Why not 8 or 9? **URL:** \ **Category:** Factual Questions\ **Created:** [August 25, 2001, 7:36am UTC](https://boards.straightdope.com/t/why-are-7-cat-years-equal-to-one-people-year-why-not-8-or-9/78070 "2001-08-25T07:36:00Z")\ **Posts on this page:** 12\ **Page:** 1
**Author:** ![Sultan\_Kinkari](https://avatars.discourse-cdn.com/v4/letter/s/7bcc69/32.png) [@Sultan\_Kinkari](https://boards.straightdope.com/u/Sultan_Kinkari)\ **Post date:** [August 25, 2001, 7:36am UTC](https://boards.straightdope.com/t/why-are-7-cat-years-equal-to-one-people-year-why-not-8-or-9/78070/1 "2001-08-25T07:36:00Z")
This was inspired by a thread about [human teeth.](http://boards.straightdope.com/sdmb/showthread.php?threadid=83660) I asked myself “Do cats and dogs or any other animals have baby teeth?” I did a lttle research and discovered the answer was _yes_. A cat’s baby teeth grow to full size by about eight weeks, and at five to six months they are replaced by permanent ones. If seven “cat years” are supposed to equal one “people year”, and if the cat gets it’s permanent teeth at six months and humans lose their baby teeth at seven or eight, wouldn’t that make one “people year” closer to 12 or 13 “cat years”? My cat lived to be seventeen, thats 119 years old by the seven-scale cat year! C’mon, no average human lives to be that old. But if we went by my baby teeth index, she would have been 221, a little fanciful. Now she was damn old, so I feel six “cat years” is about right. That would have put her at a respectable 102. What is the whole “seven year” theory based upon? The time it takes for a cat to reach full maturity? Menopause? Do tell. ---
**Author:** ![G.Nome](https://avatars.discourse-cdn.com/v4/letter/g/c89c15/32.png) [@G.Nome](https://boards.straightdope.com/u/G.Nome)\ **Post date:** [August 25, 2001, 7:46am UTC](https://boards.straightdope.com/t/why-are-7-cat-years-equal-to-one-people-year-why-not-8-or-9/78070/2 "2001-08-25T07:46:59Z")
I don’t think that idea makes any more sense than if humans estimated their ages in cat years. How many people go around saying they’re 12 (or whatever age) in cat years? Not many. ---
**Author:** ![Sultan\_Kinkari](https://avatars.discourse-cdn.com/v4/letter/s/7bcc69/32.png) [@Sultan\_Kinkari](https://boards.straightdope.com/u/Sultan_Kinkari)\ **Post date:** [August 25, 2001, 7:50am UTC](https://boards.straightdope.com/t/why-are-7-cat-years-equal-to-one-people-year-why-not-8-or-9/78070/3 "2001-08-25T07:50:09Z")
People don’t go around saying their 12 in cat years because that would make them roughly two years old, which is a little young to be grasping advanced concepts such as people and cat years, let alone “age” in general. ---
**Author:** ![23skidoo](https://avatars.discourse-cdn.com/v4/letter/2/f04885/32.png) [@23skidoo](https://boards.straightdope.com/u/23skidoo)\ **Post date:** [August 25, 2001, 7:58am UTC](https://boards.straightdope.com/t/why-are-7-cat-years-equal-to-one-people-year-why-not-8-or-9/78070/4 "2001-08-25T07:58:04Z")
The way I heard it, the “7:1” ratio was for dog-years. I also thought this was strange, because I kept hearing stories about 15, 16, 17 year old dogs. What is that… 119 years old? Yikes! Then I heard somewhere that the 7:1 ratio is not actually correct, that a better formula for “exchanging” human years into dog years is this: The first year, the dog “ages” 10 years. Every year after that, the dog “ages” 4 years. Which makes that 17 year old dog… Lessee… 74 years old. See, that number seems less alarming to me. Anyone else heard about doing the conversions this way? ---
**Author:** ![Fern\_Forest](https://avatars.discourse-cdn.com/v4/letter/f/71c47a/32.png) [@Fern\_Forest](https://boards.straightdope.com/u/Fern_Forest)\ **Post date:** [August 25, 2001, 9:49am UTC](https://boards.straightdope.com/t/why-are-7-cat-years-equal-to-one-people-year-why-not-8-or-9/78070/5 "2001-08-25T09:49:15Z")
mild guessing I think a lot of this also comes from a time when cats were so well cared for and lived harder lives and hence died, on average, earlier. And usually they just say a cat lives 10 years on average (not really but play along) and a human lives 70 on average (not really but close enough) divide 70 by 10 and that’s what they use, 7. I’m sure these aren’t the numbers anyone ever used and it was always probably a rule of thumb kind of thing. Recently more intelligent people noticed this wasn’t entirely true and came up with the one that **23skidoo** mentioned factoring in 3 data points, birth, beginning of puberty, and death. You might be able to add in a few more, like menopause for females. I don’t know though, do cats go through menopause? I’m sure they must. ---
**Author:** ![Cougarfang](https://avatars.discourse-cdn.com/v4/letter/c/c67d28/32.png) [@Cougarfang](https://boards.straightdope.com/u/Cougarfang)\ **Post date:** [August 25, 2001, 9:56am UTC](https://boards.straightdope.com/t/why-are-7-cat-years-equal-to-one-people-year-why-not-8-or-9/78070/6 "2001-08-25T09:56:05Z")
as a “cat”, i shall offer my version of enlightenment. cats live seven years for every human year because 1. seven is a lucky number (for some), 2. we cats work harder [mumble]lazy humans[/mumble] and 3. just because. tah-DAAAAAAAAAAAAAAAAAAAAAAAAAAAHHH… ow! no pineapples! ow! ow! ow! ---
**Author:** ![silent\_rob](https://avatars.discourse-cdn.com/v4/letter/s/e9a140/32.png) [@silent\_rob](https://boards.straightdope.com/u/silent_rob)\ **Post date:** [August 25, 2001, 10:00am UTC](https://boards.straightdope.com/t/why-are-7-cat-years-equal-to-one-people-year-why-not-8-or-9/78070/7 "2001-08-25T10:00:27Z")
This is a WAG, but I think it has to do with people thinking of pets (cats and dogs) as members of the family. They’re like people in more and more ways. So a dog or cat’s full life is made equivilent to a human’s through the year conversion. 15 is old to a dog or cat, so that’s made equivilent (through conversion) to what is old for a human. ---
**Author:** ![KidCharlemagne](https://avatars.discourse-cdn.com/v4/letter/k/ed8c4c/32.png) [@KidCharlemagne](https://boards.straightdope.com/u/KidCharlemagne)\ **Post date:** [August 25, 2001, 12:16pm UTC](https://boards.straightdope.com/t/why-are-7-cat-years-equal-to-one-people-year-why-not-8-or-9/78070/8 "2001-08-25T12:16:54Z")
23skiddo is right. That old rule of thumb was simply made because of the ratio of the human/dog life spans. The actual equivalent is completely non linear. I dont remember the actual comparisons, but i know the early years are much higher relative to the later years. 7 is just the average. ---
**Author:** ![bibliophage](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bibliophage/32/7615_2.png) [@bibliophage](https://boards.straightdope.com/u/bibliophage)\ **Post date:** [August 25, 2001, 3:05pm UTC](https://boards.straightdope.com/t/why-are-7-cat-years-equal-to-one-people-year-why-not-8-or-9/78070/9 "2001-08-25T15:05:31Z")
It is non-linear as others have said above. The Perfect Master speaks (about dogs, specifically) here: [Is it true one “dog year” equal seven “human years”?](http://www.straightdope.com/classics/a2_010b.html) ---
**Author:** ![postcards](https://avatars.discourse-cdn.com/v4/letter/p/8e8cbc/32.png) [@postcards](https://boards.straightdope.com/u/postcards)\ **Post date:** [August 25, 2001, 7:36pm UTC](https://boards.straightdope.com/t/why-are-7-cat-years-equal-to-one-people-year-why-not-8-or-9/78070/10 "2001-08-25T19:36:29Z")
[Calculator](http://www.stupid.com/games/dogyears/) [Edited by bibliophage on 08-25-2001 at 02:43 PM] ---
**Author:** ![postcards](https://avatars.discourse-cdn.com/v4/letter/p/8e8cbc/32.png) [@postcards](https://boards.straightdope.com/u/postcards)\ **Post date:** [August 25, 2001, 7:37pm UTC](https://boards.straightdope.com/t/why-are-7-cat-years-equal-to-one-people-year-why-not-8-or-9/78070/11 "2001-08-25T19:37:34Z")
Guess I forgot how to do this sort of thing. Sigh. Cut and paste. Sorry. ---
**Author:** ![NutWrench](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/nutwrench/32/20193_2.png) [@NutWrench](https://boards.straightdope.com/u/NutWrench)\ **Post date:** [August 25, 2001, 11:22pm UTC](https://boards.straightdope.com/t/why-are-7-cat-years-equal-to-one-people-year-why-not-8-or-9/78070/12 "2001-08-25T23:22:38Z")
And what’s even worse is that it takes _seven_ cat dollars to equal _one_ people dollar! –Nut _It takes a big man to cry, but it takes a bigger man to laugh at that man_