How to calculate cat age

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:

Cat Age Select Age

Where Indoor-Only Indoor & Outdoor Outdoor-Only

Your cat's age in human years

Early maturation

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.

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?”

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

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

When we get a kitten, we fall in love with them into adulthood and senior years. Over time, we pet owners learn how to take care of our cats from beginning to end, understanding the ins and outs of spaying and neutering, bathing and vaccines, and weight management and food preferences. We quickly learn that there are different stages of development that cats experience, requiring us to care for them in new ways. Luckily, we have the ability to understand our cats' development more easily when we have a general idea of what their age is in human years.

There are several methods that allow cat owners to convert their pet's age, and the following process utilizes averages. In other words, development changes from cat to cat. Some purebred cats, like the Maine Coon, mature much slower than others and don't reach full development for three or four years. Like humans, cats age in relation to genetics, diet, exercise, care at home, and veterinary care. For example, a kitten can be six or seven weeks old but appear to be far more advanced physically over a human baby of the same age.

Regardless of the chart's averages, it's worth it to get an idea of how old your beloved cat truly is in human years:

1. First, allow 15 human years for the first year of your cat's life.
2. Then, add 9 years for the second year. For instance, a 2-year-old cat will be approximately 24 human years.
3. Next, add 4 human years for each successive year of your cat's life.
4. Finally, refer to the accompanying cat-age-to-human-age chart to double check your calculation.

When calculating the age of your cat in human years, it's important to recognize that various factors may affect your cat's comparative age to that of a human. This may include variables such as heredity, diet, environment, and physical and medical care. While it's probable that you don't have any say over heredity, you do have options for controlling other factors that have an effect on your cat's aging process. For instance, if you have a senior cat, you can provide them with special needs by performing a weekly physical, brushing hair and teeth daily, and feeding them proper nutrition.

If, however, you have a kitten, you can pay attention to key development stages in the first eight weeks. The first week, you'll want to understand that your kitten will be born with eyes closed and ears folded, and weight will be somewhere between 90 to 100 grams. Around day three, you can expect the umbilical cord to fall off. After seven days, weight should double. Ensure that in week two your kitten's eyes open and baby teeth begin to form. In the third week, ears become pointed and a few kittens will start to explore the environment. By week four, you can expect some more teeth and better hearing. In weeks five to eight, you can expect your kitten to see fully, try to eat solid food, and a change in eye color and activity. During this time, you should prepare for your kitten's first vaccination.

Cats of all ages should be closely monitored when it comes to things like development, food, and vaccinations.

Determining your cat's age usually isn't an issue if you had your kitten since birth. However, if you had a rescue cat or a stray, you may be unsure. The first thing you can do is look at teeth. For instance, if you see baby teeth emerging it's likely a kitten. If, however, you notice that there's staining from tartar, it's probable that your cat is an adult or senior cat.

You can also look for additional signs of sexual maturity. If a male cat is spraying urine or showing their testicles, it's likely around 5 months of age and experiencing puberty. Female cats around this age will go through heat, which you will be able to see and hear. Look for other signs like coat development and eyes.

Up until six months old, your pet is considered a kitten. Then, it goes from kitten to junior up to two years old. Around three to six, your cat enters its prime years of development, before moving into the mature stage of life, around seven to 10 years old. When your cat finally reaches its senior age (11 to 14 years old), care begins to change more dramatically. In fact, your cat's life begins to change even more so during the geriatric stage, when reaching a whopping 15 years of age and older.

Your cat can live for a long time, depending on lifestyle. Consider if your cat is an indoor or outdoor cat, for instance. Some wild cats live for about four to five years, while many indoor cats live for about 13 to 17 years. Despite this, it's not unusual for an indoor cat to live up to a long 20 years. If your cat is overweight, however, they are likely to live between 12 and 15 years old.