How Old is My Cat in Human Years?

Last week was a fun week, because I got to see a lot of old cats. Really old cats. You see, I really like the geriatrics. I feel that cats give us so much entertainment when they're young and crazy, and so much love and companionship during their bulk of their lives, while requiring relatively little maintenance. When they get old and more dependent on us, I feel it is time for us to give the love back. I guess my reputation as a geriatric-cat lover has gotten around, because people keep bringing me the oldies, and I love it! Today I saw Dino, aged 19 yrs, 3 months. He's got kidney disease (mild) and hyperthyroidism (controlled), and he looks absolutely great for his age. The real kicker was last Friday. I examined Carlota, aged 20 years, 4 months. She's got glaucoma in one eye, asthma, and chronic renal failure. She's tiny and frail, but totally adorable. The funny thing is, she wasn't the oldest cat in the hospital that day. While I was examining her, Jake was relaxing in our boarding ward downstairs. Jake is 21 years, 4 months, and has been a patient of mine for years. His owner travels a lot, so Jake boards with us a lot, and of course we've grown super-fond of him over the years. Every time he feels a little under the weather, we panic a little, but before we know it, he bounces right back. This cat is going to live forever. So... exactly how old is "old"?

I confess, one thing that drives me crazy is when people who own a 20 year old cat say, "That's like a person being 140." Um, no it's not. The notion that dogs (and cats) age seven years for every one year is a myth that’s managed to stick around for years. If you think about it, it is not uncommon for some cats to live to be 18 or 19 years old. If they aged seven years for every one year, then an 18-year-old cat would be equivalent to a 126-year-old person, which is clearly not very likely. In my own veterinary practice, there are at least 10 cats who are over 20 years old, but there are certainly no 140-year-old people. The “seven-to-one” rule is just not true. Cats age faster when they’re younger, but this slows down as they get older. At 6 months of age, a female cat already can reproduce. So, at what age can a person reproduce? Let's be conservative and say 15. At 1 year of age, cat bones fully stop growing. This occurs in people at approximately 24 years of age, give or take a few years. So, a 1-year-old cat is roughly equivalent to a 24-year-old person. From that point on, cats age approximately three to four years for every one year. Or so I thought.

Here's the ORIGINAL chart that I made. It was based on my personal opinion and experience:

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I based the above chart on the fact that 20 year old cats used to be about as rare as 100 year old people. But, since I graduated vet school, advances in veterinary medicine have resulted in cats living longer than ever before. And as you can see from my story last week, I had three cats that were just around 20 years old. So, here's my REVISED chart. Again, it's not an exact science, but I think it's probably reasonably accurate:

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Hopefully, cats will continue to live longer and longer lives. I would love nothing more than to revise this chart over and over again.