(by Andres Rojas)

It’s hard to say at what age cats are considered adults. Indeed, adult cats maintain a youthful appearance throughout their life that makes judging their age difficult to discern.

Moreover, contrary to popular wisdom, 1 cat year isn’t the equivalent to 7 of ours. Instead, as Dr. Jeff explains:

“Cats are considered adults typically by a year of age. They are growing so fast that usually by 8-10 months they're full-sized, sometimes they fill out a little bit more later. Certainly by the age of 2...I would say they are young adults (teens) maybe at 1 and by the age of 2 they are pretty much full adults.”

Since your cat’s diet and age should correspond, it helps to understand how kittens develop into adult age.

What a Cat’s Youth Looks Like

Compared with humans, kittens grow incredibly fast. 

According to a guideline by the American Animal Hospital Association (AAHA), cats reach puberty in just about 7 months.

This is what your kitten’s journey into adulthood looks like:

• 1 month: is about the same as a toddler’s first year.
• 2-3 months: is equivalent to 2-4 human years.
• 4 months: by 4 months your kitten is as developed as a 6-8 year-old child.
• 6 months: your kitten is as mature as a 10-year-old kid.
• 7 months: your kitten has just entered its rebellious years and is now a 12-year-old in human years.
• 1 year: your kitten has reached 15, in human years, and is about to stop growing.
• 1 1/2 years: at 18 months (21 in human years), your cat has become an official adult.
• 2 years: is equivalent to 24 in human years.

After your cat’s second year, each following year of your cat’s life becomes about the same as 4 human years.

Kitten Age vs. Maturity

Although calculating the months and years can give you a good idea of your cat’s growth rate, it isn’t a perfect system for estimating a cat’s-to-human age. If you aren’t sure about your kitten’s age, your veterinarian can estimate your cat’s age by comparing its physical development with other cats of the same breed.

As a general rule, most kittens are considered fully grown by their 12th month of age. 

However, there are smaller breeds that mature even faster than that – Munchkins can reach their adult size in just 9 months - while large breeds, like the Maine Coon or Norwegian forest cats, can take up to 2 years to stop growing!

Just like with humans, a kitten’s maturing rate is primarily determined by their diet, genetics, and sex – female cats reach sexual maturity earlier than males.

Finally, a cat’s growth might be delayed or even stunted depending on how early (if at all) the cat is spayed or neutered.

If you have doubts about your kitten’s age, talk to a veterinarian you can trust.

When Is Your Cat Ready to Eat Adult Cat Food?

Giving your cat the right type of food at each life stage is essential for your pet’s health.

Kitten food is heavy on protein, fats, and other nutrients that they need to grow and build a healthy immune system.

However, once the big stretch is over – usually by their first birthday – you should start feeding adult cat food to your cat to avoid obesity and other health issues.

Some large breeds, like Maine Coons, that take longer to grow may benefit from a kitten diet for longer. In most cases though, it’s better if you buy a food packet that is within your cat’s age range.

Take at least a week to transition to cat food to avoid stomach issues - and, as always, check with your veterinarian if you need further advice about which cat food to get.

Got More Adult Cat Care Questions?

Visit Dr. Jeff Werber’s Instagram account (@werbs_dvm) to view and submit questions and answers on weekly AMAs – or call and leave a voicemail at 424-835-0576. Your call will be returned posthaste. For emergencies, download Dr. Jeff Werber’s app Airvet, a video-chat option for veterinary needs at any time of day or night!