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When is a Cat An Adult? From Kitten to Fully Grown

For humans we generally have quite obvious milestones for when a child becomes an adult. This could be the age they are allowed to drive a car, drink alcohol, get married etc and across the world this tends to range from 18 to 21 years.

But when is a cat an adult? We don’t have those types of legal milestones for our favourite felines. How do you know if your cat is an adult? And if they are an adult what thing should you change and what things should stay the same?

Find out how to think about age when it comes to cats, the move from kitten to cat, what you need to change and what you need to look out for in this post.

Two tabby kittens


When is a Cat an Adult – Key Milestones for Cats

Rapid Growth: 2 to 6 Months

The rapid growth stage begins once a kitten is weaned off its mother. At this stage, the kitten needs lots of nutrients to support its fast rate of growth. Kittens need twice as much energy as adult cats on a per pound basis

However, their mouths and stomachs are much smaller than that of an adult cat. This means that it is best for kittens to have several small meals a day rather than 1 or 2 large meals.

white kitten with blue eyes

Adolescence: 6 to 12 Months

Your cat’s growth will begin to slow down during this stage and it can be moved to 1 to 2 meals a day. Kitten food is still the best option for cats in this phase as despite their growing size they are still in need of a high level of nutrients.

Cat rolls around in the sun why do cats roll in the dirt

Young Adult: 6 months to 2 years

This is the phase during which your cat moves from kitten to adult.

Prime Adult: 3 years to 6 years

Cats are settled into their lives and in their prime.

Mature Adult: 7 years to 10 years

Cats tend to become less active during this time and health issues more likely to arise.

norwegian forest cat tabby green eyes starting at camera when is a cat an adult
A green eyed Norwegian

Senior Cat: 11 years to 14 years

The life spans of cats vary quite a bit but this is essentially old/older age for felines.

Most experts agree that cats become adults at 12 months of age. However, they may not reach their full size until anywhere between 18 months and four years.

When is a Cat an Adult vs Full Size – Important Factors to Consider

1. The Cat Breed

The average age for a cat to move from kitten to adult is between 10 and 12 months. However, this is just an average. Longer-haired and larger breeds like Maine Coons and Siberians become adults between 15 and 18 months.

maine coon tabby cat staring with very pointy ears

This is because larger breeds obviously have to get larger to reach maturity – and most long-haired cat breeds are larger. Maine Coons are the largest of all cat breeds and can take up to four years to reach their full size.

Siberian Neva masquerade cat
Siberian Neva masquerade cat

2. Diet

If kittens don’t receive the proper nutrients their growth can be stunted.

Lazy Cat Eating Big Bowl of Food

3. When was your Cat Been Spayed or Neutered?

Studies have shown that cats spayed or neutered earlier in life tend to grow larger than cats that are not spayed or neutered until they become adults.

A neutered cat’s ability to burn calories is modified and it can gain weight quickly. As your newly neutered cat will most likely be hungry there may be more meowing for food. It is important to monitor your cat’s feeding in the 18 week period after being neutered so as to avoid unnecessary weight gain or the creation of bad habits.

ginger maine coon cat

4. Indoor Cats vs Outdoor Cats

Indoor cats tend to be larger than outdoor cats. This is because they tend to be better fed can can’t roam as far or exercise as much as outdoor cats. Outdoor cats may often be physically smaller than indoor cats but tend to be in better shape.

Indicators that your Cat has reached Full Size

The best way to tell if your cat has reached full size is by through its weight, height and length. The easiest way to do this is to measure the weight, height and length of your cat each month.

tabby kitten with leash on scales

Top Tip: If you’d like an indicator of how big your cat will end up being take its weight at 16 weeks and double it. This won’t be a perfect measure but will give you a feel for their potential size.

When is a Cat an Adult – Food

Like humans, your cat’s nutritional needs will change as they age. Your cat’s health will be influenced by whether or not their bodies received the right nutrients at the right time.

One of the biggest times of change in nutritional needs for cats is when they move from being kittens to being adult cats.

vet puts grey cat on scales

When should I start feeding my kitten adult cat food?

Once your cat has reached 12 months of age it is time to start moving them to adult food. Adult cats need less food as they are not as active as kittens. The combination of their growth slowing down and being neutered can also slow down their metabolism.

As a result, adult cat food tends to be lower in fat and protein.

Note: If your cat has been neutered it may be better for your kitten to transition to adult food sooner. Do check with your vet.

grey cat on scales

How do I move my cat from kitten food to cat food?

It isn’t a good idea to move your cat from 100% kitten food to 100% adult cat food. Instead, transition your cat’s type of food intake over several days. Not only will this help your cat to accept the new food it will also decrease the chance of any issues with their digestion of the new adult cat food.

Young cat eating at home from its bowl. Female hand adding food

On the first day put 75% kitten food and 25% adult food into your cat’s bolw at each meal. On day two move to 50% kitten food and 50% adult food. Day three 75% adult food and 25% kitten food. And then on day four move to 100% adult cat food.

If your cat is struggling to adjust then slow down the percentage move to adult food and manage the transition over a larger number of days.

hungry cat eating from the food bowl

Free-choice feeding is fine for most cats as they tend to only eat what they want. This involves allowing them access to food 24/7.

Personally, I have dry food available for my cat 24/7 and two set times a day for when it receives wet food. Portion-controlled feeding can be better for indoor cats as they tend not to be as active as outdoor cats.

two Scottish kittens lap milk from bowl

Dog Years vs Cat Years vs Human Years

It is often interesting to compare our own ages to that of our cats. Cats age most quickly in the first year of their life. These guidelines have been created by the American Animal Hospital Association:

  • A cat at one month is the equivalent of a human at one year.
  • A cat at three months is the equivalent of a human at four years.
  • A cat at twelve months is the equivalent of a human at fifteen years.
  • A cat at eighteen months is the equivalent of a human at twenty-one years.
  • A cat at two years is the equivalent of a human at twenty-four years.
  • At the age of three years, a cat is the equivalent of a human at twenty-eight years. From the ages of three to eleven add four human years for each additional cat year.
  • At eleven a cat is the equivalent of a sixty-year-old human. Then continue to add four human years for each additional cat year.
long haired white cat being measured

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Thursday 14th of March 2024

Many veterinarians advocate scheduled, portioned feeding rather than free feeding to avoid obesity. They also favor wet food over dry as cats feed dry diets can be more prone to diabetes and kidney disease.

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