Comparing cat and dog ages with human age in a table (and more)

It is perhaps quite interesting to compare how both cats and dogs age in comparison to humans. You’ll see a lot of cat age charts compared to human age and likewise you’ll see the same for dogs but how about a direct cat to dog comparison?

There are complications! There would be wouldn’t there. Firstly, you’ll see different charts from different sources. For instance, Purina say that cats age at the same rate as dogs in their comparison with human age. It is very confusing and perhaps misleading or it might be the case that we are simply unsure. And the usual, well-publicised 7:1 (cats to humans) ratio is no longer considered to be accurate as it is too linear.

One issue is that cats and dogs age a different speeds compared to humans at different stages of their lives. It is not a liner comparison as mentioned throughout the cat or dog’s life. Also larger dogs age faster and have shorter lifespans in general than smaller dogs although the French bulldog due to an extraordinary list of genetically inherited health problems has the shortest lifespan (7 years) of all the domestic dogs based on a recent study.

Here is a table based on the American Kennel Club for dogs and the Daily Mail and PetMD websites for cats. I have selected dogs of a similar weight to cats to make the comparison meaningful. But for instance a giant dog weighing 100+ pounds would be the human equivalent of 79-years-of-age at the age of 10 and 121 in human years at the age of 17.

I discuss the cause of speeded up aging in cats and dogs after the table.

Why do cats and dogs age faster than humans?

The heading above might be slightly misleading and deliberately so to emphasise the point. Cats and dogs don’t age faster than humans in a strict sense but their lifespans are generally shorter compared to humans because of their accelerated life processes.

In addition to what I’ve said below about size affecting lifespan, dogs and cats attain adulthood at a much faster rate than humans. They grow more rapidly in their early years which places stress on their bodies which leads to shorter life spans.

And I would like to emphasise the issue of selective breeding or artificial selection which I mention below. This leads to a predisposition to genetically inherited health problems carried by recessive mutated genes which on average lead to shorter life spans.

And then there are the environmental hazards that are suffered by cats and dogs over and above those that affect humans. For example, outdoor cats in America can suffer from predation by coyotes and of course there is the ever present road traffic accident which kills many cats.

Veterinary care and nutrition: There is a big argument on the Internet about the domestic cat’s diet and commercially prepared cat food which isn’t always the most healthy. It is said, for example, that dry cat food can lead to Type II diabetes sometimes. Also, the ever popular, cheap dry cat food can exacerbate the possibility of developing cystitis. Commercially prepared cat food is not always an optimal diet which can affect health and longevity.

It is probably fair to say that cats and dogs are treated less well than humans. Although, it has been said that dogs are treated better than cats by humans. But humans are prone to speciesism which means cats and dogs are devalued slightly which in turn must impact lifespan ultimately.

Within the breeds, dogs buck the trend that larger animals live longer

The dog breeds buck the trend that the larger animals live longer which is what happens in nature. But nature is dictated by natural selection whereas the dog breeds are created through artificial selection and this totally upsets nature’s way.

The larger the dog the shorter their life expectancy. For instance, the Saint Bernard will have a lifespan of between 5-8 years while the smaller breeds generally have a lifespan of around 12-15 years. But as mentioned above, even that general trend is overturned by extraordinary inherited health problems which are suffered by, for instance, the French Bulldog which has a lifespan of around seven years.

Larger animals live longer than smaller animals

In general, despite the complexities, larger animals tend to live longer than smaller ones. There are exceptions and variations. The key reasons why there is this general tendency is because:

Metabolic rate. Larger animals have slower metabolic rates compared to smaller ones which means the body is working at a slower rate which in turn lends itself to longer life spans. The ageing process is speeded up the small animals compared to larger animals.

Energy reserves. Larger animals normally have greater fat stores and therefore greater energy reserves which are able to sustain them when food is scarce. This adds a survival advantage leading to a longer lifespan.

Environmental pressures such as predation upon the animal. Smaller animals are far more vulnerable to being attacked by larger animals and killed for their food. Predators are often large animals and they prey upon the small ones. This naturally extends their lifespan. And some large predators are at the top of the pile. They are apex predators with no other animal to kill them. The lion comes to mind in Africa. And the jaguar in South America.

Reproductive strategies. Slower reproductive rates and longer reproductive cycles benefit larger animals. This allows them to put more time and effort into raising their offspring which helps their survival which in turn increases, on average, their life spans.

There are exceptions such as some small animals having longer life spans than some larger animals. It’s a complex issue.

Dr. Bruce Fogle DVM’s age calculator

As somewhat of an afterthought, I would like to add into this page Dr. Bruce Fogle’s cat-to-human age calculator from his book Complete Cat Care.

He usefully adds in some younger ages. For instance, he says that a one month old cat is like 10 months of age in human terms. A cat of three months of age is equivalent to 7 years of age in a human while a cat of six months of age is the equivalent of nine years in human terms.

A cat of three years is 42 years in human terms. A cat of 20 years is 93 years in human terms. You can read more about Dr. Bruce Fogle’s age calculator by taking on this link.