Dogs in GeneralLarge DogsSmall Dogs

How old is my dog in human years? Avoid the old wives tale.

1 dog year is not 7 human years

This is an age-old question, and as a dog owner one that I have asked many times. I was one of those people who succumbed to the general belief that 1 human year equals 7 dog years. But this is really one of those old wives tales!

1 dog year is not 7 human years

This general rule of thumb has been around for generations, and to be honest I can’t even remember where I got the information from. It seems that it’s one of those myths you grow up with and it just sticks with you. Just like dog hair on your favorite jumper!

How did this urban myth come about?

Very easily and the maths really is common sense if you look at it carefully. Around the 1950s people really started taking an interest in the ages of their canine companions, an average human lifespan was around 70 years old. An average lifespan of a dog was assumed to be around 10 of our years.

And what’s 70  divided by 10? You’ve got it, 7. Hey presto, you have your general rule of thumb. i.e. that a human year is 7 dog years!


Why isn’t it true? Because it’s just not that straightforward…

Hoe can I tell my dog's real age?The life cycle of a dog is very different to our own. Their rate of growth early on is a lot quicker than a humans. This does make sense and you will have seen it in your own dog during the first year of their life.

When you bring home your brand new puppy, they are definitely a small bundle of fun and very much a baby animal. But I’m sure you’ve seen the time-lapse photography, or series of images, that show how rapidly they grow during that first year. Before you know it, they have really passed through the toddler stage and are well into the teenage-canine phase. If you picture them at a year old, it’s quite likely they are full of energy, still get up to mischief and may be a bit enthusiastic and clumsy at the same time. Just like a human teenager who hasn’t quite grown into their own body yet!


How in fact does it work?

There are slight variations around, and some of the dog food companies are very keen to give out dog-age calculators, but my advice would be to take care with these. It’s possible there may be a marketing angle that influences when they think it’s time for you to use specially classed types of food related to your dog’s age.

The true way to tell a dog's age

The best formula I’ve come across is from the American Veterinary Medical Association. Who better to look at these age patterns than those that specifically study the canine form? They do provide a general guide, bearing in mind that dogs are all slightly different and their ageing pattern may be influenced differently by their own genetic makeup, environmental factors and their individual lifestyle.

As a basic guide though, for a medium sized dog

  • the first year of their life is equivalent to about 15 of ours. Hence the reference to gangly teenagers above!
  • the second year is equivalent to roughly 9 human years
  • after that stage, an approximate guide is about 5 human years for every further year in a dog’s life.


However, what about large dogs? Or in fact small ones? How does it differ for them?

Example of a big dogThis is a bit of a confusing one. Why? Because in the animal kingdom, it’s generally accepted the larger the mammal, the longer they live. Think blue whale or elephant!

However, when we look at dogs the opposite is usually true. It’s the small dog breeds that tend to outlive the larger breeds. Even scientists admit this is a bit of a nature conundrum, and that more study is required to try and find out why this is the case.


example-of-a-small-dogOne theory at the moment (and we all know these can change with any new study!) is that large breed dogs grow at a very accelerated rate at a young age. This very quick growth may make them more susceptible to age-related illnesses later on in life. There are also some suggestions that this rapid growth may lead to greater numbers of abnormal cells, which in turn can lead to cancers and disease.

It’s also true that large dogs are less able to cope with some age related illnesses, and in particular joint and bone problems. Many large dog owners, including me, have witnessed hip displaysia and/or arthritis. It’s no surprise that a bigger dog is less able to cope with these type of problems, due to their size.

  • They are heavier, which puts additional pressure on their joints.
  • They are further from the ground, so any difficulty getting up or laying down are emphasized
  • They are less likely to be carried around, like smaller dogs, so the damaged joints can be subject to additional wear and tear even earlier

You can read more here about how dogs also have a stoic attitude to these problems, so it can be a long time before you may notice they are having problems.

Our dog enjoying his walks at 11
Our dog still enjoying his walks at age 11!

When I think back to our German Shepherd, who had hip and elbow displaysia, plus arthritis, he still bounced around with his tail wagging whenever the lead came out. He could also still pull me around if there was a particularly tasty smell in a bush, and all this at the grand old age of 11! But at the same time he was on daily pain medication and joint supplements too – at least they must have been helping a bit!!

Just as large dogs have accelerated growth in early development, some scientists also suggest that their decline is also quicker in later life. To quote an evolutionary biologist Dr Cornelia Kraus “their lives seem to unwind in fast motion”. Based at the University of Göttingen in Germany, she has a particular interest in studying why large dogs seem to die at a younger age. You can see more about Cornelia here.


A helpful chart to tell the human age of your dog

In summary, it’s not quite as simple as a straightforward “one size fits all” mathematical formula. I particularly like this helpful chart from the American Kennel Club website. It’s the best chart I have come across, that caters for small, medium and large dogs.

Chart to help calculate your dog's age in human years

What do you think? Maybe you have your own ideas or have come across other helpful ways to tell your dog’s age. Either way, please feel free to leave your views below. It would be interesting to see what other people think – especially since the scientists don’t seem to be 100% sure all of the time!


4 thoughts on “How old is my dog in human years? Avoid the old wives tale.

  1. I found this really fascinating! I had also wondered why so many dogs seemed to be living to be so old! Although I don’t have a dog, I am fascinated by eyes and when dogs have cataracts their pupils are so large you can often see the white glint of the cloudy lens.

    Nowadays in a healthy human cataracts start in the 70s and are usually operated in the 80s (obviously there is a large range of ages and it also depends on whether the person has other systemic issues). What is the usual age where a dog will need cataract surgery?

    1. Hi Brian and thanks for your comment. The most common cause of cataracts in dogs is genetic inheritance and this type can occur at any age. It may also affect different breeds in varying degrees of severity. Age-related cataracts are a lot less common, but tend to occur at age eight or older – and that’s eight of our years! Cataracts may require diagnosis by a specialist ophthalmic vet as well. Not all vets have the relevant equipment to determine the condition. However you should always visit your usual vet first, who can then refer your dog for specialist examinations if necessary. This was a very good question you asked. Have a great day, Mara

  2. This is news to me! I have always believed the 7 year rule. This explains how dogs seem to live to be over 100 years old. Thanks for sharing this new way to more accurately determine a dog’s age.

Leave a Reply

Your email address will not be published. Required fields are marked *