It’s generally assume that dogs mature faster than humans. As a result, some humans try to interpret dog years on a linear human scale. According to this convention, a dog ages seven years for each human one.
Pets/WebMD takes a more nuanced approach. It assigns more human years at the beginning of a dog’s life then adds diminishing amounts near the back end. By this method, a one year old puppy is a teenager and a seven year old dog is middle aged. This tells us that Pets/WebMD has never met a seven year old dog.
Others prefer to place dog years on logarithmic scales. (They’re called nerds).
My formula works this way: for each year your dog has been alive, that’s how old he is. Pommie Jones has been with us three years, that means he three. He’s not 21; he’s not 28; and he’s certainly not whatever the nerds at San Jose State think he is. A dog may mature more quickly than a human, but he spins around the earth at the exact same pace.