Dog 1
3 years 27.4 human years
Mature Adult
20% of expected lifespan15 yr average
Monitor weight closely, begin annual baseline bloodwork, maintain regular exercise
Side-by-side
Compare your dogs
Two dogs born on the same day can be at completely different points in life. At three, a Chihuahua has lived about a fifth of its expected lifespan; a Great Dane the same age has already used up more than a third of its own, and will be a senior at six.
Dog 2
3 years 30.8 human years
Young Adult
35% of expected lifespan8.5 yr average
Transition to adult food, establish dental care routine, discuss spay/neuter timing
Why size changes everything
Through their first five years, dogs of every size convert identically. From year 6 the paths split: each additional calendar year adds about 4 human years for a small dog but nearly 8 for a giant breed. Compounded over the following decade the gap is enormous — at 10 years old a small dog is around 56 in human terms while a giant breed is around 79. To run it the other way, see how old you would be as a dog.
The percentage bars above use each breed's average lifespan, which is often the more useful number for care planning. It tells you when to expect the shift to twice-yearly vet visits, senior diets and joint support. See the full chart or run a single dog through the main calculator.
How the comparison tool works
Each dog card runs the same engine as our main calculator, independently and entirely in your browser — nothing you enter is sent anywhere.
- Identify the dog. Pick one of 91 breeds, which loads its average lifespan and the age it typically turns senior. For a mixed breed or an unknown breed, choose a size instead.
- Set the age. The slider runs up to 25 years in quarter-year steps, so you can compare a 9-month-old puppy with a 12-year-old senior.
- Read the four results. Every card shows the human-equivalent age (calibrated to the breed’s lifespan when a breed is chosen, or the AKC size chart otherwise), the life stage, the share of expected lifespan already lived, and a care tip for that stage.
What a side-by-side comparison reveals
Here is what the tool shows for three popular breeds that are all 10 years old:
| 10-year-old | Human age | Life stage | Lifespan lived |
|---|---|---|---|
| Chihuahua | 51.1 | Mature Adult | 67% |
| Labrador Retriever | 57.5 | Senior | 80% |
| Great Dane | 78.2 | Geriatric | 118% |
The Chihuahua has a third of its life still ahead. The Great Dane has already outlived its breed’s average. That gap, not the human-year number alone, is what should shape a dog’s diet, exercise and screening schedule.
Multi-dog homes by the numbers
Comparing dogs is an everyday question for many owners. The average dog-owning household in the US keeps 1.6 dogs, a figure that has held steady since 1987, according to the AVMA. With dogs now in 71 million US households, or 53% of all homes (APPA), millions of families care for two or more dogs at once, often of different sizes and ages.
Those size differences are large. In more than 13 million dog records from Banfield Pet Hospitals (Montoya et al., 2023), small purebred dogs had a life expectancy at birth of 13.5 years against 9.5 for giant breeds — a four-year gap. Face shape matters too: in a UK study of 584,734 dogs (McMillan et al., 2024), small long-nosed breeds had a median lifespan of 13.3 years, while medium flat-faced breeds reached only 9.4. Two dogs that joined your family together may well need senior care years apart.