Figuring out the human age of your dog just got a lot trickier.

Turns out the conventional wisdom that one dog year is equivalent to seven human years has no basis in science. It's a myth but a good one that's lasted centuries.

It's myth first recorded some 800 years ago. An example of the seven year rule of thumb is an inscription at Westminster Abbey dating back to 1268. This estimates one human year is equivalent to nine dog years.

Like Us on Facebook

Researchers have long recognized this seven year rule of thumb doesn't make any scientific sense. As far back as 1953, a French researcher published a more scientific version of the rule based on empirical evidence.

What he suggested was that dogs age 15 to 20 times faster than humans do during their first year of life. This ratio, however, is reduced to about one dog year being the equivalent of five human years. So, it looks like a five-year rule of thumb.

But it's also not as simple as that, however. Larger dog breeds tend to pass away well before smaller ones. A 10-year-old small dog is about 56 years-old in human years.

Some breeds like beagles have different aging ratios than their same-sized counterparts in different breeds.

The reason dogs can reach full sexual maturity after one year of their birth is because dogs also age faster during the first two years of their lives than humans do.

Other researchers noted that if humans actually age seven times slower than dogs, many of us would have children at age seven and live to be 150 years old. That's patently not so.

So, what's one to believe? The table below is probably the best guide available to determining just how old your beloved mutt is.