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Cat Years To Human Years: A Guide To Calculating Your Cat's Age

Est. read time: 10 min.

You’ve probably heard that one dog year is equivalent to seven human years, but is the formula really that simple? The conversion formula for both dog and cat years to human years is actually much more complex. Because both of these animals mature at a faster rate than humans, the first years of your pet’s life actually equate to more human years than the subsequent years. To get a better idea of how cat and human ages equate, use our cat age calculator:


Your cat's age in human years

Why cats mature early

Your feline companion is your precious baby, we know, but you must remember that cats are still animals. They are still much closer to their wild roots than us bipedal humans.

A primary example of this is the way that humans have evolved to have long gestation periods and then even longer periods of intensive rearing and childcare. Domesticated house cats have a gestation period of only 66 days and give birth to kittens that require just a small portion of the kind of attention and care that human babies require. And the little bit of work they do require can be done with a self-cleaning litter box.

That’s why a one-year-old kitten is the developmentally equivalent age of a 15-year-old human, and the physical maturity of a two-year-old cat is roughly equivalent to a 25-year-old human. Then, for each year after the first two, equate each cat year to about four human years. That would make a 5-year-old cat about 36 human years old.

If you’re having trouble grasping early maturation in cats, look at this way: Kittens do most of their growing in the first 6 months of life. In fact, healthy kittens grow 8 times their size in just about 8 weeks! By approximately 1 year old, cats will weigh at or around their adult weight, which typically ranges from 7 to 15 pounds depending on the breed. 

How do you know when your cat has stopped growing? Most veterinarians agree that your cat is done growing between 9 months and 2 years old. However, some breeds take years to fully mature. Learn more about cat life stages, according to American Animal Hospital Association (AAHA).

An alternative formula

Tracie Hotchner, author of "The Cat Bible," offers a slightly different variation on the aforementioned calculation. In this alternative formula, Hotchner delves more specifically into the corresponding ages of young kittens to similarly young human children. Here, courtesy of Hotchner, is the answer to the question, “How old do cats live in human years?”

  • A 1-month-old kitten is equivalent to a 6-month-old human baby
  • A 3-month-old kitten is equivalent to a 4-year-old child
  • A 6-month-old kitten is equivalent to 10 human years old
  • An 8-month-old kitten is equivalent to a 15-year-old human
  • A 1-year-old cat has reached adulthood, the equivalent of 18 human years
  • A 2-year-old cat is equivalent to a 24-year-old human
  • A 4-year-old cat is equivalent to a 35-year-old human
  • A 6-year-old cat is equivalent to a 42-year-old human
  • An 8-year-old cat is equivalent to a 50-year-old human
  • A 10-year-old cat is equivalent to a 60-year-old human
  • A 12-year-old cat is equivalent to a 70-year-old human
  • A 14-year-old cat is equivalent to an 80-year-old human
  • A 16-year-old cat is equivalent to an 84-year-old human

cat years to human years

Cat years to human years: The indoor vs outdoor factor

If you used our cat years to human years calculator above, you might be wondering why you had to specify whether your cat is indoor-only, outdoor-only, or a mix. The sad fact is, a cat’s environment largely influences their lifespan. Ask a veterinarian and they’ll tell you: Cats that go outside are more at risk of harm or injury.

Just as ancient man lived outdoors and had a life expectancy of 20-30 years, outdoor cats face exposure, predators, harsh conditions, and chronic “wear and tear” that can ultimately lead to a shorter life expectancy. Indoor cats are the modern equivalent of pampered, sheltered royalty when compared to outdoor cats or even indoor/outdoor cats.

Speaking of indoor/outdoor cats: Even if 90-95% of your cat’s life is indoors, your veterinarian still needs to know about the small percentage of time spent outdoors. Why? Because it affects how they care for your cat and what diagnostics, vaccines, medications, and treatment they may use.

So, why is a 5-year-old indoor cat in the prime of his life (36 years old in human years) while a 5-year-old outdoor cat has already entered middle age (48 years in human years)?

Why outdoor cats “age” faster

There’s a difference between an outdoor cat with no home (i.e. feral or stray), and a cat with a loving home that just happens to live outside. The former’s lifespan is adversely affected by lack of vaccinations and routine vet visits, as well as not being spayed or neutered. But even if your outdoor cat is vaccinated, sees the vet regularly, and is spayed or neutered, there are still a lot of risks with living outside.

First, being outside poses trauma dangers. Your cat might get hit by a car, attacked by a dog or coyote, injured by the neighborhood bully, or beat up by the neighborhood tomcat. Veterinarians report trauma as the #1 issue seen in a veterinary ER with indoor/outdoor cats. Trauma can result in fractures, lung bruises, internal bleeding, and even death. And if you’re lucky enough to save kitty’s life, treatment may cost several thousands of dollars for repair. 

Next, being outside poses poisoning dangers. Something as simple as your cat eating your neighbor’s tiger lilies or daylilies, digging around and finding some mouse poison, or accidentally being exposed to antifreeze in your neighbor’s driveway can result in death. 

Finally, the outdoors pose infection or disease transmission risks that can potentially be fatal to your cat. Fighting with other cats can easily result in your cat getting the blood infection feline leukemia (FeLV) or kitty AIDS/FIV. (Learn more about FeLV and FIV at Cornell Feline Health Center.) Also, if your cat goes outside, the risks of tapeworms, fleas, ticks, and other parasites dramatically increase. It’s extremely important that your outdoor cat be vaccinated and up-to-date on their FeLV and rabies vaccines, along with year-round flea, tick, and heartworm medication. 

How old is my cat?

If you adopted your cat, you may not know their exact age. However, knowing the age of your cat can be important for you to properly care for them. Here are some characteristics to look for to help you estimate your cat's age:

  • Fur: Kittens and young cats usually have soft and smooth coats whereas older cats might have thicker, coarser coats. You might even notice some grey in an older cat's fur.
  • Teeth: Kittens usually don’t get all their teeth until around 6 months of age, and younger cats tend to have much whiter teeth. You will likely notice increased wear and tartar build-up the older your cat gets. 
  • Eyes: Young cats may have brighter eyes and older cats may have cloudier eyes (but this is not always the case).
  • Hormonal changes: As early as 5 months of age, an unspayed female kitten might start going into heat. Signs include territorial marking, mating calls, or wanting to escape outdoors.
  • Mobility and activity levels: Older cats tend to move less and be less playful than younger cats. Less activity can also contribute to more weight gain in older cats.

Learn more about how to tell how old your cat is.

Two ways to look at age

Though the common perspective on cat years and human years is trying to figure out how old our cats are in human years, that conversion can be applied both ways.

That is to say, if you consider the maximum age of a human to be 100 years, then, based on the Cat Calculator, the maximum age of a cat is 20.8 years. On the other side of the coin, if you consider that, as The Cat Bible suggests, 16 human years is comparable to 84 cat years, then a 100-year-old human could be said to be the equivalent of 525 cat years.

Though this is a generally less practical way to consider the relative aging rate, it does serve as an important reminder… The way we experience time, the length of our human years, and the meaning we assign to certain-numbered years (the big 3-0, for example), is a matter of perspective. Some other oft-quoted ideas come to mind: "It’s not the years in your life, but the life in your years" and "You’re only as old as you feel."

How old is your cat according to the cat years to human years formula? Or perhaps we should ask, how old are YOU in cat years?

Photo by Manja Vitolic on Unsplash