How old is a 20-year-old cat in human years?

different cat ages cartoon

A 20 year old cat is equivalent to being 96 years old in human years. However this is not an accurate way to know a cat’s actual age in human years.

You also need to observe behaves physically and cognitively, and physical signs; also diet, exercise, vaccinations, supervision outside, detoxification.


If you thought that there was a purely scientific way to know how old a 20-year-old cat is in human years, you would be wrong.

Up to now, scientists have not come up with an agreed, reliable method of calculating how many cat years equal how many human years and vice versa.

This article shows how to really know how old your 20 year old cat is in human years.

Using it you can get a pretty accurate idea, keeping in mind that it is not exact.

1. Physically, cat years are not equal to human years

In other words, it’s not a 1:1 relationship. A 20-year-old cat is not 20 years old in human years.

International Cat Care, including their veterinary division, The International Society of Feline Medicine (ISFM) have set up a feline-human age scale.

Note that this scale represents physiology, not cognitive maturity. In other words, how the body is maturing, not the brain.

The International Cat Care scale is represented in the chart below.

As the chart shows, the first six months of your cat’s life is the time when it ‘ages’ the most.

So, by the time a kitten is six months old, it is 10 years old in human terms.

During the next stage, Junior, things slow down a bit. By the end of this stage, a two-year-old feline is 24 years old.

To get a feel of the slower rate: if the 2-year-old junior cat would have continued to age at the same rate as in the kitten stage, it would be 40 years old, not 24.

For those who want the math: if a six month old cat = 10 human equivalent years old, then a cat aged 2 (which are 4 x 6 months) = 4 x 10 human equivalent years or 40 years old.

From the Adult to the Super Senior stages (basically the remainder of the cat’s life), the age difference slows down.

Each feline year (not month) is equivalent to roughly four human years.

cat age in human years table

International Cat Care very kindly let us use this chart from their site.

2. Feline age can also be measured by behavior

A 20-year-old (human years) cat does not behave like a 20-year-old human.

Well, ok, cats don’t behave like humans, but I think you understand my meaning.

That is, 20-year-old humans are relatively young in human terms. They are starting to be adults, just beginning their independent lives.

What about a 20-year-old cat?

The International Cat Care Organization describes six feline life stages.

I will describe them using the stage names from the chart above.


This is a time of rapid (very fast) growth. Usually, kittens are not fully mature sexually.


Cats grow to their full size during this time.

They also learn the ins and outs of life as they experience it and how best to survive their environment.

Obviously, an indoor-only cat’s life skills will be somewhat different than those of an indoor-outdoor or totally outdoor cat.


As the name suggests, this should be the best time in a cat’s life.

They have reached physical and behavioral maturity. They should still be healthy and active.

As a result, they are able to enjoy life fully.


To get an idea of a feline at this stage, consider a human in their mid-40s to mid-50s.

They are usually settled, with a clear path in life. They have achieved quite a lot, but may still have goals and dreams on their to-do lists.

Same for felines. While they are more worldly wise and set in their ways, there are still surprises left…for them and for you.


The way a cat is during this stage very much depends on its health.

If the cat is reasonably healthy with no major problems, then it will continue to enjoy a good life—albeit with occasional ‘aches and pains’ requiring visits to the vet.

Unfortunately, cats with poor health have difficult times, and may end their days here.

However, in the U.S., the estimate is that “20 percent of pet cats are 11 years of age or older.”

Overall, good chances for a long life.

Super Senior

Again, depending on its health, a cat will have a good (or not so good) stage of life.

So, a 20-year-old cat is actually quite a long-lived, senior feline.

Respect to the cat and the carer!

3. Brain function is another aspect of how ‘old’ a cat is

cat psychology metaphor

Like in humans, it’s not just how many years the cat has been alive, which measures how ‘old’ it is.

The DISHA group of signs is a way that veterinarians measure cognitive decline (less brain function) in dogs. It is also used for cats.

D: disorientation – The cat does not recognize familiar people and/or gets lost in known surroundings.

I: interaction changes – Pet-owner social interactions are different than before. Pet-pet interactions change. Examples are more needy or more distant, calmer, or more irritable.

S: sleep/wake disturbances – Your cat’s sleeping patterns change. Perhaps more awake during the night or more sleepy during the day.

H: house-soiling – The litter box is not the only place kitty is doing its ‘business.’.

A: activity changes and anxiety – The cat is less interested in playing, is generally more inactive, and/or the cat is more restless, showing repetitive anxious actions such as licking, an increase in vocalization (meowing), and a need for more attention.

Another sign added recently is learning and memory.

If your cat cannot do tasks that it has already learned (such as finding hidden food or successfully completing feline food puzzles), it means that something is happening with the brain.

If your relatively young cat is showing DISHA signs, it is recommended to visit your vet.

It could be that your cat is just aging faster than normal.

However, there could be some medical issues that need attention.

4. Estimate the human years of your cat by looking at physical signs

This method is especially useful when adopting stray cats or other cats whose birth dates are unknown.

There are four main physical signs.

Check out the teeth

cat mouth wide open to see teeth

Kittens generally get their first teeth at 2-4 weeks old. At four months, they begin getting their permanent set.

Thus, a full set of white teeth indicates a cat of about 1 year old.

As the cat ages, tartar builds-up on the teeth and staining increases, although if the owner is good about brushing his or her pet’s teeth, this will be much less.

So, a bit of yellowing could mean a cat aged 1-2. Lots of tartar might point to a cat of 3-5.

If teeth are missing, the cat is probably mature or senior (names according to the chart in #1 above), although cats that have had rough lives may lose teeth earlier.

Look at the muscle tone

The higher activity levels of younger cats tend to give them more muscle definition.

If the cat is bonier, has protruding (sticking out) shoulder blades, and/or has some loose, hanging skin, you are likely dealing with an older cat.

Feel the coat

fur closeup

Is it soft and fine? Think kitten or junior.

Thicker and coarser? Probably adult or mature.

Grey hair or even patches of white? Senior or super senior.

Peer into the eyes

closeup of cat to see eyes

The eyes of younger cats are clear and bright. There is no discharge (stuff leaking from the eyes).

The iris (colored part) will generally be smooth. Older cats tend to have more jagged irises.

If there is cloudiness in the eye, the cat is most likely at least 12 years old.

Having said all that…

Changes in your cat’s iris could also be due to a medical condition and not just normal aging.

If you see a discharge or cloudiness, time for a checkup at the vet.

5. Human years are not the only aging factors in cats

Two cats may both have lived for 20 human years, yet their behavior and health are completely different.

One of the cats may look and behave like a ‘young’ 20-year-old cat and the other has more of a ‘senior’ quality.

Most of this can be explained by their lifestyles, environments, and the care they receive.

The five main factors to keep your cat in optimum health are diet, exercise, vaccinations (perhaps not what you think!), supervision, and detoxification.


If your cat lived in the wild, its prey (live food) would have a lot of protein, minerals, and be about 70% water (the human body is about 60% water).

Your pet cat’s diet should have these same components. This means high moisture (water), top-quality meat, some good condition animal fat, not too many carbohydrates.

One expert recommendation is a raw diet. Balanced raw diets can be homemade or commercial.

All this is bad news for cats whose diets are primarily dry food.

If your cat prefers dry food, here is the first part of a two-part expert article on a program to gradually move your pet to a healthier diet.

Since feline diets can be species-specific, it is best to ask your vet for guidance. You can also read about feline nutrition at reliable sites such as Feline Nutrition.


Just as in humans, extra weight on a kitty brings a variety of negative health conditions.

Here are some ideas to keep your pet at healthy weight and fitness levels.

Bring back the ‘hunt’

Instead of food bowls, hide your cat’s food in a food-dispensing mouse. This seems to be the only company which is offering them at the moment.

What’s nice about this idea (in my opinion) is that the cat has to actively search for the food and then ‘open’ it—exercise for the body and the brain.

Walk the cat

walking a cat using a leash

This link has 20 recommended cat harnesses to consider.

I must say that I tried this idea with some of my cats years ago. None liked it.

Yet, I know many people whose cats just love taking a walk—especially indoor-only cats.

Since it’s not a very expensive investment, I think it is worth a try.

Encourage climbing

Think multi-level cat climber, not beds and bookcases.

These recommendations are not only good exercise, they also give your pet a safe, command post.

This can also help with feline bullying.


I found that there is some difference of opinion among experts about which vaccines to give and how often they are needed.

Core Vaccines

The consensus (agreement) is that kittens need the core vaccines:

  • Rabies
  • FVRCP:
    • FVR/FHV-1 (Feline Rhinotracheitis Virus/Herpesvirus 1)
    • FCV (Feline Calicivirus)
    • FPV (Feline Panleukopenia)

Kittens should receive a set of three FVRCP vaccines: 6-8 weeks, 10-12 weeks, 14-16 weeks.

Then, they should get a 1-year FVRCP booster.

The rabies vaccine is given at 14-16 weeks, with a booster at one year old.

kitten vaccination


While the general recommendation is for annual and/or 3-year vaccines (depending on the disease), there are experts who feel that re-vaccination is more of a risk than a benefit.

They say that indoor-only cats and outdoor-supervised cats only need the kitten vaccines.

The re-vaccinations could cause a severe allergic reaction to the vaccine (vaccinosis) as well as be a danger for cats that have other health conditions (allergies, organ problems, cancer/cancer survivor, hormone issues, etc.).

Read more about vaccinosis here.

Non-core vaccinations

There are a variety of additional vaccines that are considered optional depending on your cat’s general health and lifestyle.

Your overall best bet is to consult with your vet to develop a personal vaccine program for your kitty.

Outside supervision

Cats should always be supervised when outdoors.

One form of supervision is a closed-in play area in your front or back yard/garden.

Another is your being in attendance while your cat is outside to see what kitty is doing—in the same way you would monitor a toddler.

Outdoor cats are much more likely to be exposed to diseases from other animals.

They are also at a higher risk of poisoning from plants, chemicals, etc.

Sometimes, cats hide in problematic places such as the wheel well of a vehicle or up inside its hood.

Then, there is the issue of fighting. Even winners often have scratches, bites, and bruises.


cat fitness and detox

This is where your cat is exposed to poisonous substances beyond your control.

Examples include heavy metals in unfiltered water, radiation from natural and artificial sources, electromagnetic fields (EMFs), and home and environmental chemicals.

Another category of potential toxins are the traces of hormones and antibiotics in pet food, not to mention preservatives and a variety of allergenic ingredients.

Even the products used to keep cats healthy (such as flea and tick solutions, vaccines, medications, etc.) have some percent of chemicals that are hard on the body.

The expert recommendation is to regularly detox your cat.

Before you run out and buy some type of detox product, read this.

Many of the steps in a good detox program are common sense. They involve making limitations or substitutions, do-it-yourself ideas, and are based on common ingredients which you probably have at home already.

So, no need to start spending money needlessly…and sometimes a lot as these specialty items can be quite expensive.

Bonus: More expert care

No disrespect to your vet, yet there are vets and then there are vets.

As in every profession, some people are better than others.

If you feel that you could be getting better veterinary service, check out the links below.

Hospitals and animal doctors dedicated to the excellent health and care of pets:

Cat Care for Life – a comprehensive program for optimum cat health:

More about the ‘blueprint’ + finding a cat-friendly clinic


Writer: Lisa Aharon

lisa aharon