Most pet owners think their dogs are a lot younger than they are according to scientists

who have developed a new formula for working out a pet's age in human years.

A one year old dog is actually about 30 on our scale, not the seven that is commonly assumed.

The idea you just have to multiply it by seven is a myth - as it is is much more complicated, according to new research.

The new sliding scale has a four year old dog in its early fifties and by the time it's nine it's in its mid sixties.

Their more accurate technique is based on the rate at which chemicals are added to genes - known as the DNA 'clock'.

It works across breeds - and could also be used to assess anti-ageing creams, according to new research.

Senior author Professor Trey Ideker, of the University of California, San Diego, explained: "There are a lot of anti-ageing products out there these days - with wildly varying degrees of scientific support.

"But how do you know if a product will truly extend your life without waiting 40 years or so?

"What if you could instead measure your age-associated methylation patterns before, during and after the intervention to see if it's doing anything?"

Enfield Independent:

To calculate your dog's age in "human years" based on epigenetics, find the dog's age along the bottom axis and trace your finger straight up until you reach the red curve. Then trace your finger straight over to the left to find the corresponding human age..

The study looked at how dogs aged by focusing on DNA methylation - marks that change over time as a cell matures.

It involved blood samples from 105 Labrador retrievers. As they grow older dog genes pick up molecules known as methyl groups - known as 'epigenetic' changes.

The method described in Cell Systems is based on the changing patterns of methyl groups in dog and human genomes as they get older.

Since the two species don't age at the same rate over their lifespans, it turns out it's not a perfectly linear comparison, as the 1:7 years rule-of-thumb would suggest.

The formula provides a new 'epigenetic clock' - a method for determining the age of a cell, tissue or organism based on which genes are "off" or "on".

Epigenetic changes provide scientists with clues to a genome's age - just like wrinkles on a person's face, said Prof Ideker.

His team and other researchers have previously published epigenetic clocks for humans that don't translate to other species.

It was geneticist Dr Tina Wang who brought the idea to him while working as a student in his lab.

Prof Ideker said: "We always look at humans, but humans are kind of boring. So she convinced me we should study dog ageing in a comparative way."

Dogs are an interesting animal to study, he said. Man's best friend's environmental and chemical exposures are very similar - and they receive nearly the same levels of health care.

It's also important we better understand their ageing process as veterinarians often use the old 1:7 years ratio to determine a dog's age.

They use that information to guide diagnostic and treatment decisions, said Prof Ideker.

What emerged is a graph that can be used to match up the age of your dog with the comparable human age. This is not a 1:7 ratio over time.

Especially when dogs are young, they age rapidly compared to humans. A one-year-old dog is similar to a 30-year-old human.

A four-year-old dog is similar to a 52-year-old human. Then by seven years old, dog ageing slows.

Prof Ideker said: "This makes sense when you think about it - after all, a nine-month-old dog can have puppies, so we already knew that the 1:7 ratio wasn't an accurate measure of age."

Since it's accurate for humans and mice as well as Labrador retrievers, he predicts the clock will apply to all dog breeds.

Next, the researchers plan to test other dog breeds using saliva samples.

They also want to see what happens to the epigenetic markers of mice when you try to prolong their lives with a variety of interventions.

Meanwhile Prof Ideker, like many other dog owners, is looking at his own canine companion a little differently now.

He said: "I have a six-year-old dog - she still runs with me, but I'm now realising that she's not as 'young' as I thought she was."