How old is your dog in human years? This tool converts dog years to human years with a size-adjusted estimate instead of the old x7 rule, and shows your dog’s life stage.
Dogs mature fast in their first two years, then larger breeds age more quickly than smaller ones.
An estimate only – real aging varies by breed, genetics and health. Your vet is the best guide to your dog’s life stage.
How Old Is a 5 Year Old Dog in Human Years?
A 5 year old dog is about 36 to 45 in human years, depending on size. A small dog comes out at about 36, a medium dog at 39, a large dog at 42 and a giant breed at 45. The first two years count as 24 human years for every dog, and size only matters after that.
Dog years chart by size
| Dog age | Small | Medium | Large | Giant |
|---|---|---|---|---|
| 1 yr | 15 | 15 | 15 | 15 |
| 2 yr | 24 | 24 | 24 | 24 |
| 3 yr | 28 | 29 | 30 | 31 |
| 5 yr | 36 | 39 | 42 | 45 |
| 7 yr | 44 | 49 | 54 | 59 |
| 10 yr | 56 | 64 | 72 | 80 |
How Dog Years Are Calculated
The first year counts as roughly 15 human years and the second as about 9 more, so every dog is around 24 by its second birthday. After that, each dog year adds a set number of human years based on size: about 4 for small dogs, 5 for medium, 6 for large and 7 for giant breeds.
- Start at 24 human years for a 2-year-old dog.
- Count the dog years past 2. For a 5-year-old, that is 3.
- Multiply by the size rate: 3 × 6 = 18 for a large dog.
- Add it on: 24 + 18 = 42 human years.
So how old is a 3 year old dog in human years? Between 28 and 31, because only one year of size-based ageing has kicked in.
Small Dog Age in Human Years vs Large Dog Years
Small dogs age more slowly once they are grown. A 10-year-old small dog is about 56 in human years, while a giant breed the same age is closer to 80. Large dog years to human years run at about 6 per year after age two, which is why the x7 rule (70 at age 10) makes an older small dog too old and an older giant dog too young.
How to Use the Dog Age Calculator
- Enter your dog’s age in years (decimals are fine for puppies).
- Choose its size category by adult weight.
- Read the result. The human-age equivalent and life stage appear straight away.
Have a cat too? See our Cat Age Calculator.
Picking the right size and age
Size drives the result more than anything else, so pick the group for your dog’s expected adult weight, not its current weight. A five-month-old Great Dane is giant.
- Mixed breeds: go by adult weight. If your dog sits between two groups, try both and treat the answer as a range.
- Rescue dogs: a vet can estimate age from teeth and other signs; use that as your starting point.
The life stage label goes by age alone: puppy under 1, young adult to 3, adult to 7, mature to 10 and senior from 10. Large and giant breeds tend to reach their senior years sooner, so they may need senior check-ups, joint care and diet changes earlier.
Watch for slowing down, stiffness, cloudy eyes, confusion or weight change, and raise them with your vet rather than putting them down to age. The aging in dogs article on Wikipedia explains why size matters so much.