Dogs also reach reproductive age sooner than humans do. By eighteen months old, most dogs are full grown and capable of reproducing, but using the old formula, an eighteen-month-old dog would only be equivalent to a ten-year-old human, and they’re still far from adulthood. So is there a better way to calculate a dog’s age in “human years”? It can be useful to understand what health problems may occur as they age, and when to expect certain changes in their bodies and behaviors. There isn’t one formula that works for all dogs, but there are several good calculators online that factor in breed or size. Your veterinarian can also provide advice to help your dog live a long and healthy life.