Let's say you step outside to retrieve your mail one day and there is a friendly cat sitting on your stoop. You decide to give your new feline companion a proper home. It’s a likely scenario and one that occurs every day.

Beyond giving the cat a name and scheduling a checkup, you will want to determine an approximate age of the cat to ensure it receives adequate nutrition.

What Is A Cat Year In Human Years?

According to a Fox News article, the world’s oldest cat recently hit a milestone of 30 years in age. Based on average comparative lifespans, that would put "Rubble" the British house cat at around 137 in human years.

But, Rubble is an enigma; an indoor cat typically doesn’t make it beyond 20 years in age. So there are admittedly some flaws in relating a cat year to a human year. For one, cats reach puberty in as little as 5 to 6 months after birth. Secondly, the oldest human in recorded history only made it to 122 years in age.

So, while it’s fun to use tools such as Pet Pattern’s Cat Age Calculator, it is admittedly flawed. Go ahead and enter your feline’s age into the calculator and then read on for a few more scientific approaches.

Estimate A Cat’s Age: What To Look For

Veterinarians use a variety of methods to determine a feline’s age. Pet Pattern has listed a few of these observational methods so you can have a rough idea if one so happens to show up on your doorstep one day.

Baby Teeth (2 - 4 Weeks)

Within two to four weeks of age following birth, kittens’ baby teeth will start to emerge. If you find a stray kitten that you would like to take home with you, checking for teeth (or lack of teeth) can tell you a lot about its dietary needs.

Kittens should receive breastmilk from their mother (or formula) for at least the first two months of life.

Eye Color Changes (6 Weeks)

As in humans, cat eyes will often change from a baby blue hue to a more permanent pigment color. This happens as the kitten begins to produce more of its own melanin. In some cat species, the pigmentation of eyes never changes and will always remain some shade of blue.

Emergence Of Adult Teeth (3 - 4 Months)

Around three to four months of age, a cat’s permanent, adult teeth will begin to displace those “deciduous” baby teeth.

Feeling The “Heat” (5 - 6 Months)

Cats reach puberty in just five to six months. So, if you do find or adopt an adolescent cat, you should start planning to have them spayed or neutered as soon as possible. It’s not only good for a cat’s physical health, but their psychological health, too! Plus, you will avoid the issues with spraying, running away, and excessive meowing.

A cat’s gestation period is only 65 days. This means a female cat can have a full litter of kittens by the time she is only 8 months in age! Before they start penning love letters to that calico down the road, schedule an appointment to have your cat “fixed.”

Thicker Fur (6 - 12 Months)

Around 6 months to 12 months in age, cats will shed their soft baby fur and a denser, coarser coat will emerge. The color of the fur will also likely change, either becoming lighter or darker in color.

Belly Paunch (2+ Years)

At around two years in age, most cats’ physique will change (regardless of gender). Around this time, a majority of cats will develop a “paunch,” which is sort of like a hanging, flabby belly that even occurs in the healthiest, most active cats.

Tartar Buildup On Teeth (2+ Years)

As they get on in years, cat teeth will typically have more tartar buildup around the gum line. But, tartar buildup may also be an indication that a cat is eating too many soft foods and/or their oral health has been neglected. Your veterinarian can make recommendations on a proper oral health routine for your feline friend.

Eye Health (Senior Years)

In younger cats, the lens of the eyes is clear and vibrant. But as cats approach their senior years (roughly 8-10 years in age), their ocular health begins to diminish. The eyes may exhibit signs of cataract or a clouding of the eyes. Older cats will also have some tearing or discharge around the eyes, especially near the canthus (corner of the eye).

Aging In An Outdoor Cat

It is said that outdoor cats age twice as quick as indoor cats. So a cat that have spent a considerable portion of its lifetime outdoors may appear to show signs of an indoor cat twice its age. Relative to human years, one year of an outdoor cat's life is roughly 8 years. Beyond all the hazards (cars, predators, other cats, etc.), felines face a lot of wear and tear outdoors.

An indoor cat can be expected to live anywhere from 15 years to 20 years, but an outside cat may only make it to 10 years of age — if they’re lucky. The Humane Society states that most cats left to roam outdoors typically don't make it beyond five years in age.

How Do You Calculate Cat Years?

A cat's age is estimated at the equivalent of twenty-five human years when they reach two years of age.

After reaching two, each additional year is an extra four cat years.

According to Fox News the world's oldest cat managed to live to thirty years and three days which would have been the equivalent of 137 in human years.

Use our cat age calculator to find out how long your feline has lived for.

Of course, the calculator doesn’t quite go that high, but how do you guesstimate a cat’s age?