Ages 1–20 by body size
Compare dog years to estimated human years for small, medium, and large dogs. The chart accounts for fast maturity during the first two years, then uses size-based estimates through age 20.
| Dog Age | Small Dog | Medium Dog | Large Dog |
|---|---|---|---|
| 1 year Young Adult | 15 | 15 | 15 |
| 2 years Young Adult | 24 | 24 | 24 |
| 3 years Adult* | 28 | 29 | 30 |
| 4 years Adult | 32 | 34 | 36 |
| 5 years Adult | 36 | 39 | 42 |
| 6 years Mature* | 40 | 44 | 48 |
| 7 years Mature* | 44 | 49 | 54 |
| 8 years Senior* | 48 | 54 | 60 |
| 9 years Mature* | 52 | 59 | 66 |
| 10 years Senior* | 56 | 64 | 72 |
| 11 years Senior | 60 | 69 | 78 |
| 12 years Senior | 64 | 74 | 84 |
| 13 years Senior | 68 | 79 | 90 |
| 14 years Senior | 72 | 84 | 96 |
| 15 years Senior | 76 | 89 | 102 |
| 16 years Senior | 80 | 94 | 108 |
| 17 years Senior | 84 | 99 | 114 |
| 18 years Senior | 88 | 104 | 120 |
| 19 years Senior | 92 | 109 | 126 |
| 20 years Senior | 96 | 114 | 132 |
*Size matters: The label beside each year is only a general reference. A large dog may enter mature and senior stages earlier than a small dog. Breed, health, and individual development can shift every timeline.
Find your dog’s chronological age in the first column, then move across to the size category that best matches the dog’s expected adult weight. Small means 20 lb / 9 kg or less, medium means 21–50 lb / 9.5–23 kg, and large means over 50 lb / 23 kg.
The number in that cell is an estimated human-age equivalent. It offers a clearer comparison than multiplying by seven, but it is not an exact statement about health or longevity. For decimal ages or dogs under one year, calculate your dog’s age with the interactive tool.
Puppy describes the fast first-year period of growth, learning, and development. Young adult generally covers early adulthood after puppyhood. Adult is the established middle period, while mature signals a transition toward later-life needs. Senior is a broad later-life category, not a diagnosis.
These stages overlap and differ by size. In the model used here, large dogs reach later stages earlier, medium dogs sit between, and small dogs tend to move through adult stages more gradually.
Dogs of different adult sizes do not always share the same aging pattern. The chart keeps ages one and two consistent across sizes—about 15 and 24 human years—because early maturity is rapid for all dogs. After age two, it adds four human years per dog year for small dogs, five for medium dogs, and six for large dogs.
Those rates are a practical comparison model, not an official medical formula. Breed, genetics, activity, diet, health care, and living conditions also influence how an individual dog ages.
No chart can determine a dog’s exact biological age. A useful chart reflects rapid maturity in the first two years and different adult aging patterns by size, while acknowledging breed, health, and individual variation.
In this model, a 10-year-old dog is approximately 56 human years for a small dog, 64 for a medium dog, or 72 for a large dog.
They can. After the first two years, large dogs generally move through later life stages sooner than small dogs. Individual aging still depends on much more than size.
No. The seven-to-one rule overlooks how quickly dogs mature early in life and how adult aging patterns differ. It is easy to remember but not a useful model for most dogs.
Disclaimer: This chart provides a general educational estimate and is not a substitute for veterinary advice. A dog's health or biological age cannot be determined from chronological age alone.