Calculating dog years to human years  

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The Seven Year Rule – also known as the Rule of Paw – refers to the popular belief that every calendar year a dog lives through, is equivalent to seven human years. It’s an idea that’s been widely held by many for years, and one that scientists have never actually backed with any clinical evidence. The fact is, while dogs do age quicker than humans, different breeds and sizes will experience largely different rates. For instance, smaller dogs tend to live longer than larger ones.  

How to calculate a dog’s age in human years 

We looked into the most accurate way of converting a dog’s age into human years, in order to debunk the rule of seven. The American Veterinary Medical Association had the clearest breakdown:  

  • 15 human years is equivalent to the first year of a medium-size dog’s life 
  • The second year of a dog’s life equals around nine human years  
  • After that, each human year is equivalent to approximately five dog years  

The science behind it all 

This formula is based on a number of scientific studies, all of which heavily explored the changes in a dog’s DNA over its lifespan.  

One such study was carried out by Ideker and colleagues, which focused on Methylation – the natural biological process that occurs to the DNA throughout ageing within mammals. The study found that Methylation occurs much faster in a dog’s earlier years than it does it later years, where it slows down considerably.  
 
While this particular study was conducted on Labrador Retrievers, all dogs (no matter what breed) follow a similar developmental trajectory. Dogs reach puberty between 10 and 18 months and die before the age of 20. 

When these scientists compared the Methylation seen in Labradors with the Methylation seen in humans, they established that within a dog’s first year of life, the same mutations take place that typically take 31 years in humans. That means, by the time a dog reaches one in its biological age, they could be the equivalent of 31 years old in human years. 

As the Methylation begins to slow after a dog’s first year, so too does the ageing process. The study found that, although Methylation slowed down, it still occurred at a rate faster than that seen in humans. 

The four stages of a dog’s life 

The biological age of a dog can vary as we know, depending on the size and specific breed of dog. That said, establishing which which stage of life your dog is at is fairly straightforward. 

Just like humans, a dog’s life cycle features specific stages which they transition through as they get older. Dogs transition through the different stages of their life cycle at different speeds, and the rate of ageing is determined by factors such as genetics, nutrition and wellbeing
 
While humans go through nine life stages, canines experience just four. And as dogs experience and complete their life cycle at a much faster rate than humans, it’s even more important to really cherish the different stages. These are:  

  • Puppy 
  • Adolescent  
  • Adult 
  • Senior 

Let’s explore each life stage. The age a dog hits each will depend on the breed.

Puppy – 0-18 months 

The puppy stage begins at birth and lasts up until six to 18 months old, depending on the breed of dog. Puppies have no sight or hearing at birth, and cannot regulate their body temperature.  
 
All this starts to change at two to four weeks, when they start to open their eyes, stand up and move around. As their senses begin to develop and their curiosity expands, they will start to take in their surroundings and discover new things on their own. 

Things to consider at the puppy stage 

  • Vaccinations – your pup’s at its most vulnerable to diseases at this stage, so it’s important to keep on track with any necessary jabs 
  • House training – this is the optimum time for a puppy to learn  

Adolescent dog – 6-18 months

Adolescence is the second stage of a canine’s life cycle, and will occur anytime between the ages of six and 18 months, depending on your dog’s breed. At this stage, your dog’s a lot like a human teenager, and will be experience a number of changes, including transformations on the hormonal and physical fronts. 

Things to consider at the adolescent stage 

  • Behavioural changes – you may notice your dog ‘acting out’ in a similar way to a human teen. Attention span will be short, and you may have to deal with some disobedience. The key? Persevere with training at this point  
  • Sexual maturity – at this stage your dog will have reached sexual maturity. Female dogs will go into heat and be able to have puppies for the first time, and males will start to mark their territory by sniffing and/or urinating 

Adult – one to six years

Your dog will reach the adult milestone at between one and six years old. You’ll be happy to know things should be more manageable at this point, as your dog will be used to its environment and behaviour should have settled!  

Things to consider at the adult stage 

  • Ageing – your dog may start showing some signs of ageing at this point. He or she may be less playful, sleep more and seem to be slowing down a little on walks   

Senior – six to 10 years

Your dog’s golden years will occur between the ages of six and 10, and it’s the stage where everything starts to slows down. You’ll likely notice that your dog is sleeping more, may be stiffer in the body and slower to move. 

Things to consider at the senior stage 

  • Exercise – keep walks short and sweet. Little and often as opposed to long treks 
  • Dental issues – pay close attention to your canine’s pearly whites at this stage, as dental problems are more common with senior dogs. Be mindful of what toys they’re chewing, as well 
  • Stiff joints – older dogs are likely to experience joint stiffness as decay and muscle weakness set in. Try a supplement designed for older joints to improve mobility and aid comfort 
  • Vet check-ins – as your dog nears the winter of his or her life, it’s crucial to stay on top of check-ups  

A summary

Different breeds and sizes of dogs will age at very different rates. And while the Seven Year Rule is, in fact, a myth, it is true that dogs age at a considerably faster rate than humans. All the more reason to cherish every moment!


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  1. My boy is a rescued shih Tzu/lassa apsa
    He is 13years 8 months old. He had doggie Dementia, losing his eyesight and hearing but he is a very unique dog as no vets can handle him but if I am with him they can do blood tests anything that is needed.

  2. Thankyou for this information,it’s very enlightening! I have two senior pugs 13 and 11.
    This will help me understand more of how to help them!