Kitten math


We adopted kittens this week, within 24 hours of arriving home.  This was the culmination of several months of deciding whether or not it was a good idea given that we already have two adult cats who weren’t actually asking for younger siblings.  So far, the kittens are happy, one adult cat is curious and I think will be fine, and the other adult cat has at least progressed to the point where she’ll eat snacks right by the doorway to the room the kittens are primarily staying in.

Anyway, the place we got them from advertises that one adult female can produce 420,000 offspring over 7 years.  That seemed a little high, so I decided to check the math.

The first thing to wonder about was how to count offspring.  Clearly this was more than just kittens:  it must be counting all future generations.  But predicting how many offspring males can sire was difficult, because it really only takes a few males to father a LOT of kittens.  So I decided to initially look only at the female lines.

In looking around, it seems that cat pregnancies last about two months, and a female can get pregnant again about a month after that.  In theory this would mean 4 litters a year, but The Internet implies that most cats have 2-3 litters per year.  I decided to go with 3, since I was trying to see if that 420,000 was even resonable (as opposed to typical).

There’s also the question of how old cats have to be until they are able to mate.  It turns out to be around 6 months, though for convenience (since I was going by 4 month intervals) I decided to go with 8.  Or, looking at it another way, I figured that kittens would have their own litter on their 1st birthday (and every 4 months after that), so that’s assuming mating at about 10 months old.

Finally, there’s the size of the little.  I decided to go with 4 kittens per litter, two of which were female.

Then I made a table.  It started off like this:

0 months:  1 adult female
4 months:  1 adult, 2 (female) newborn kittens
8 months:  1 adult, 2 newborns, 2 kid-kittens
12 months: 3 adults, 2 newborns, 2 kids
16 months:  5 adults, 6 newborns, 2 kids
20 months:  7 adults, 10 newborns, 6 kids

By the end of 7 years, there were 35951 adults, 42410 newborns, and 25006 kid-kittens, leading to a grand total of 103,367 cats, including the original one, all along female-descendent lines.  If you double it in order to count the males in each litter (but no separate offspring of those males), you get around 206, 732 offspring.

Initially it sounds like the 420,000 is an overestimate, but the wording only is that cats can have that that many youngsters, not that they normally do.   If you assume that there are 3 females in each litter (all of whom procreate, etc, since this is just a ballpark estimate) you actually get 898798 offspring along the all-female lines, or over 1.5 million offspring in 7 years.   So while I doubt that having half a million offspring within 7 years is the norm, it certainly seems possible in extreme cases.


4 Responses to “Kitten math”

  1. Omar Says:

    I’ve always thought “offpsring” meant children, not descendants. Obviously here they must have meant descendants, but have you ever heard the word used that way before?

  2. Brent Says:

    But cats have been around for (at least) thousands of years, so by this reasoning the entire universe should be stuffed full of a gazillion trillion billion squillion cats. =)

  3. Ξ Says:

    Omar, because of the number I automatically translated the word as descendants (I think direct offspring would max out at 200, even in theory) but I think you’re right that “offspring” really isn’t the right word, even though several sites use that phrasing. I looked at how some other places phrased it and some used 420,000 kittens (still not quite right) or that an adult cat and her offspring can produce that many kittens (which at least gets at the idea of multiple generations).

    Incidentally, while looking for this I came across this article by Carl Bialik in the Wall Street Journal (October 12, 2006) criticizing the 420,000 figure, in part because it’s widely quoted but most people don’t know where it came from [though he traced it back to 1988, in an article citing the Humane Society]. And he himself found an earlier article in the Feral Cat Times (p. 4) that suggested a more reasonable number would be 100-400, which is at least plausible instead of only theoretically possible.

    Although even this rate of growth would lead to a gazillion trillion billion squillion cats after long enough. 🙂 I think that’s a pretty cool image, Brent, except for the whole breathing room thing.

  4. emily roselle Says:

    nice post🙂

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