How to use it
- Choose dog or cat. For a dog pick the adult size class – weight ranges and example breeds are shown under the selector.
- Enter the age in years, with months if you know them (2 years 6 months = 2.5).
- Read the human-age equivalent from the chart, the life stage, and – for dogs – the epigenetic-formula value as a second opinion.
- Scroll the chart to see how the equivalents develop year by year for every size.
Example
A 7-year-old Labrador (large): the chart gives 50 human years and the life stage is mature adult (senior from about 8 for large dogs). The epigenetic formula gives 16 × ln 7 + 31 = 16 × 1.946 + 31 = 62 – the clock runs ahead of the chart because methylation changes fastest in early life. A 7-year-old cat is 24 + 5 × 4 = 44 human years and has just become a mature adult. A 6-month-old puppy is about 7.5 chart years; the epigenetic value (20) reflects rapid early development.
Charts, formula and limits
Chart (dog, cat): year 1 = 15, year 2 = 24, then +4 (small dog, cat), +5 (medium), +6 (large, faster after year 6), giant column separate
Between whole years: linear interpolation; under 1 year: 15 × age (12 × age giant)
Epigenetic (dog): human years = 16 × ln(dog years) + 31 (Wang et al. 2020)
Life stage (dog): puppy <1, young adult, mature adult from 3–4, senior for the last ~25 % of expected lifespan
Life stage (cat): kitten <1, young adult 1–6, mature adult 7–10, senior 10+| Dog years | Small | Medium | Large | Giant | Epigenetic |
|---|---|---|---|---|---|
| 1 | 15 | 15 | 15 | 12 | 31 |
| 2 | 24 | 24 | 24 | 22 | 42 |
| 5 | 36 | 36 | 36 | 45 | 57 |
| 10 | 56 | 60 | 66 | 79 | 68 |
| 15 | 76 | 83 | 93 | 114 | 74 |
The size chart is a convention built on typical lifespans, not a measurement: it is the table published by the American Kennel Club for small, medium and large dogs, extended with the giant-breed column that circulates in veterinary practice (Purina / PetMD chart). The epigenetic clock was fitted on 104 Labrador retrievers aged 4 weeks to 16 years, so it is best for medium-to-large dogs and says nothing about breed-specific lifespan; it is not applied under about 8 weeks, where the logarithm has no meaning. The cat chart is the one used by AAHA/AAFP life stage guidelines and International Cat Care. Life-stage boundaries are rounded from AAHA 2019 (dogs) and 2021 (cats). The previous version of this page applied 15 / 9 / 4 to dogs of every size; the size-dependent chart and the epigenetic formula replace that.
Sources: Wang et al. 2020, Cell Systems – Quantitative translation of dog-to-human aging by conserved remodeling of the DNA methylome, American Kennel Club – How to calculate dog years to human years, AAHA 2019 Canine Life Stage Guidelines, AAHA/AAFP 2021 Feline Life Stage Guidelines, International Cat Care – How to tell your cat’s age in human years.
Human-age equivalents are rough comparisons for curiosity and planning, not veterinary advice. Breed, weight, diet and health change how an individual animal ages; ask your vet about age-appropriate checks.
Why big dogs age faster
Across breeds, every extra 2 kg of adult body mass shortens life expectancy by roughly a month: Great Danes rarely pass 8–10 years while many terriers reach 15 or more. The chart reflects this by adding more human years per dog year for large and giant breeds from about year six, which is also why the senior stage starts earlier for them.
Questions
- How old is a 10-year-old dog in human years?
- About 56 for a small dog, 60 for a medium, 66 for a large and 79 for a giant breed by the size chart; the epigenetic formula gives 68 regardless of size. All four are past the start of the senior stage.
- Is one cat year really seven human years?
- No. Cats mature quickly: the first year is about 15 human years and the second about 9 more, then roughly 4 per year. A 7-year-old cat is about 44, not 49, and a 20-year-old about 96.
- Which dog method should I trust?
- Use the chart for everyday comparison and life-stage planning – it accounts for size. The epigenetic formula is a research result on one breed; it is most interesting for showing that young dogs are biologically older, and old dogs younger, than the chart implies.