When is a cat fully grown?

Watching your kitten zoom around and grow bigger every day, you might wonder when they'll finally reach their full size. While most cats complete their physical growth between 12 and 18 months old, the answer isn't quite that simple — your cat's journey to full maturity involves more than just getting bigger.

When do cats reach their full size?

Most cats reach their adult size somewhere between their first and second birthdays. By 12 months old, the average house cat has typically achieved most of their physical growth, though they might fill out a bit more over the next six months. You'll notice their adult canine teeth are fully erupted around 6 months — a clear sign they're transitioning from kitten to cat.

"Cats reach skeletal maturity when their growth plates close completely, which happens around 12 months of age," Dr. Aliya McCullough, Fetch's Chief Veterinary Officer, explains. "This marks the true end of bone growth and physical development."

Do all cat breeds grow at the same rate?

Not all cats follow the same timeline. While your average domestic shorthair might be done growing by their first birthday, larger breeds take their sweet time. Maine Coons, for instance, can continue growing until they're 3 or even 4 years old — which explains why these gentle giants can reach such impressive sizes.

On the flip side, smaller breeds often complete their growth earlier, sometimes reaching their full size by 10 months. Persian, Siamese and Himalayan cats typically reach their peak weight between 6 and 10 years of age, though their skeletal growth is complete much earlier.

Physical growth vs. behavioral maturity

Even when your cat stops growing physically, they're still maturing in other ways. While their body might be fully developed by 12 months, cats don't reach complete behavioral and social maturity until they're about 2 years old. During this time, you might notice your cat becoming more settled in their personality, developing stronger preferences and establishing their adult temperament.

This extended maturation period means your physically grown cat might still act like a teenager — playful, sometimes unpredictable and still learning the ropes of being an adult cat.

When should you switch from kitten to adult food?

Since most cats complete the majority of their growth by 10 to 12 months, this is typically when you should transition from kitten food to adult cat food. Kitten food is packed with extra calories and nutrients to support rapid growth, but once your cat reaches their adult size, they no longer need that caloric boost. 

The transition should be gradual — mix increasing amounts of adult food with decreasing amounts of kitten food over about a week to avoid upsetting your cat's stomach.

Signs your cat has reached full maturity

Beyond the calendar, there are several ways to tell your cat has reached adulthood. Their proportions will look balanced — no more oversized paws or ears that seem too big for their head. Their weight will stabilize, and they won't need frequent food adjustments to keep up with growth spurts. You'll also notice their energy levels becoming more predictable, with distinct periods of activity and rest rather than the constant chaos of kittenhood.

Understanding when your cat is fully grown helps you provide the right nutrition and care at each life stage. While most cats complete their physical development by 12 months and reach full maturity by age 2, remember that every cat is unique. Large breeds might keep you guessing for a few years, while smaller cats might surprise you by reaching their adult size before their first birthday. Either way, enjoying each stage of your cat's growth — from tiny kitten to fully grown companion — is part of the joy of being a pet parent.