How dog years are calculated
Year 1 = 15 human years · Year 2 = +9 (24 total)
Each year after: small +4 · medium +5 · large +6 · giant +7
Epigenetic (2020): human age = 16 × ln(dog age) + 31
Worked example
A 5-year-old medium-sized dog is 24 human years at age 2, plus 3 × 5 = 15, for 39 human years. The epigenetic formula gives 16 × ln(5) + 31 ≈ 57, showing how much faster it thinks dogs age early in life.
Dog age chart
| Dog age | Small | Medium | Large | Giant |
|---|
| 1 | 15 | 15 | 15 | 15 |
| 2 | 24 | 24 | 24 | 24 |
| 3 | 28 | 29 | 30 | 31 |
| 4 | 32 | 34 | 36 | 38 |
| 5 | 36 | 39 | 42 | 45 |
| 6 | 40 | 44 | 48 | 52 |
| 7 | 44 | 49 | 54 | 59 |
| 8 | 48 | 54 | 60 | 66 |
| 9 | 52 | 59 | 66 | 73 |
| 10 | 56 | 64 | 72 | 80 |
| 11 | 60 | 69 | 78 | 87 |
| 12 | 64 | 74 | 84 | 94 |
| 13 | 68 | 79 | 90 | 101 |
| 14 | 72 | 84 | 96 | 108 |
| 15 | 76 | 89 | 102 | 115 |
| 16 | 80 | 94 | 108 | 122 |
Want to know your own exact age? Try the age calculator. For your dog's health, your vet is the best source of advice.
Last reviewed October 2026.
Frequently asked questions
Is one dog year really seven human years?
No. The "multiply by 7" rule is a myth. Dogs grow up much faster in their first two years: a 1-year-old dog is roughly like a 15-year-old person, and a 2-year-old is like a 24-year-old. After that, each dog year counts for about 4 to 7 human years depending on size.
Why does dog size matter?
Large and giant breeds tend to age faster and have shorter lifespans than small breeds. That is why a 10-year-old Great Dane is considered much older, in human terms, than a 10-year-old Chihuahua.
What is the epigenetic dog age formula?
A 2020 study from the University of California San Diego compared DNA changes in Labrador retrievers and people and proposed: human age = 16 × ln(dog age) + 31. It suggests dogs age especially fast when young. It was based on one breed, so it is a rough guide.
Which size category is my dog?
As a rule of thumb: small is up to about 20 lb (9 kg), medium 21–50 lb (10–23 kg), large 51–90 lb (23–41 kg) and giant over 90 lb (41 kg). Mixed breeds can go by their adult weight.
When is a dog considered a senior?
Many vets consider small dogs seniors from around 10 to 12 years, medium dogs from 8 to 10, and large and giant breeds from 6 to 8. Older dogs often benefit from more regular vet check-ups.