How old is a 3 year old dog in human years?
A 3 year old dog is between 28 and 30 in human years, depending on size. A small dog comes to 28, a medium dog 28, a large dog 29 and a giant dog 30.
Size-based chart, medium dog
- Research formula (2020)
- 49
3 year old dog in human years by size
| Dog size | Human years | Next year | Roughly like |
|---|---|---|---|
| Small | 28 | +4 | a person in their late 20s |
| Medium | 28 | +5 | a person in their late 20s |
| Large | 29 | +6 | a person in their late 20s |
| Giant | 30 | +6 | a person in their early 30s |
After the second year the size matters. Between 3 and 4 a small dog gains 4 human years and a giant dog gains 6. The 2020 research formula gives 49, above the range from the size chart.
Dog age against human age
The dots mark a 3 year old dog. Big dogs climb faster after the first two years.
Ages around 3
| Dog age | Small | Medium | Large | Giant | Research formula |
|---|---|---|---|---|---|
| 1 | 15 | 15 | 15 | 15 | 31 |
| 2 | 24 | 24 | 24 | 24 | 42 |
| 3 | 28 | 28 | 29 | 30 | 49 |
| 4 | 32 | 33 | 35 | 36 | 53 |
| 5 | 36 | 37 | 40 | 42 | 57 |
Compared with the old rule
The old rule of seven human years for each dog year would make a 3 year old dog 21. The size chart gives 28 to 30, so the old rule is 7 to 9 years too low here. Dogs age fast early on and then more slowly, and bigger dogs age faster later in life.
Questions
How old is a 3 year old small dog in human years?
About 28. Small dogs age more slowly in later years than large ones.
How old is a 3 year old large dog in human years?
About 29, and a giant dog comes to 30.
How old is a 3 year old dog if I do not know the size?
Use the size your dog will be as an adult. If you are unsure, the medium result of 28 is a fair middle guess.
What is 28 human years in dog years?
For a medium dog that is about 3 years. Try the human years to dog years calculator for any age.
Is this exact?
No. It is a general guide based on veterinary charts, and each dog ages differently. Your vet can say what the stage of life means for your dog's care.
Other dog ages
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
For any age and a size of your own, use the dog years to human years calculator. For cats see cat years to human years.
Sources
- American Animal Hospital Association (AAHA), canine and feline age chart, human-year equivalents by dog size.
- Wang T. et al., "Quantitative Translation of Dog-to-Human Aging by Conserved Remodeling of the DNA Methylome", Cell Systems, 2020 (University of California San Diego).
Last reviewed 2026-10-26.