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Dog Age Calculator

Converts a dog's age to human-equivalent years three ways: the AAHA 2019 age chart adjusted for size class (small to giant), the AVMA rule of thumb (15 for the first year, 9 for the second, 5 per year after) and the 2020 UC San Diego DNA-methylation formula 16·ln(age) + 31.

When to use

You want a dog's age expressed in human years, or want to compare the size-adjusted chart with the epigenetic-clock estimate.

Do not use when: The animal is a cat (use cat-age) or you need daily calorie needs (use pet-calories); none of the conversions is a medical assessment of an individual dog.

Formula

AAHA chart (human years at dog ages 1, 2, 3 …): small 15, 24, 28, 32, 36, 40, 44, 48, 52, 56, 60, 64, 68, 72, 76, 80, 84, 88, 92, 96; medium 15, 24, 28, 33, 37, 42, 47, 51, 56, 60, 65, 69, 74, 78, 83, 87, 92, 96, 101, 105; large 15, 24, 30, 35, 40, 45, 50, 55, 61, 66, 72, 77, 82, 88, 93, 99, 104, 109, 115, 120; giant 15, 24, 32, 37, 42, 49, 56, 64, 71, 78, 86, 93, 101, 108, 115, 123 (linear between years; under 1 year 15·age; beyond the chart the mean slope of its last four years). AVMA rule: age ≤ 1: 15·age; 1–2: 15 + 9·(age − 1); >2: 24 + 5·(age − 2). Epigenetic: 16·ln(age) + 31

The chart and rule reflect that dogs mature quickly and that large breeds have shorter lifespans. The epigenetic formula (Wang et al. 2020) was fitted to 104 Labrador retrievers and puts puppies far ahead of the chart while flattening in old age.

Inputs

Parameter	Type	Unit	Required	Description
`dog_age_years`	number	years	yes	Age of the dog in years (e.g. 0.5 for six months). Range: ≥ 0.1, ≤ 30
`size`	enum: small \| medium \| large \| giant		default medium	Adult weight class; larger dogs age faster after the second year.

Outputs

Output	Type	Unit	Description
`human_years`	number	years	AAHA 2019 chart value for the size class, linearly interpolated between whole dog years.
`avma_rule_years`	number	years	15 for the first year, +9 for the second, +5 for each year after, regardless of size.
`epigenetic_years`	number	years	16·ln(dog_age) + 31 from the UCSD Labrador methylation study; fitted for dogs of about 1–16 years.
`size_class`	string		Weight range of the selected size class.

Example

7-year-old medium dog: {"dog_age_years":7,"size":"medium"} → {"human_years":47,"avma_rule_years":49,"epigenetic_years":62.1}

4-year-old giant breed: {"dog_age_years":4,"size":"giant"} → {"human_years":37,"avma_rule_years":34,"epigenetic_years":53.2,"size_class":"over 41 kg / 90 lb"}

GET https://tttkmbb.com/api/v1/calculate/dog-age?dog_age_years=7&size=medium

Machine access

API: GET https://tttkmbb.com/api/v1/calculate/dog-age (query parameters) or POST with a JSON body {"inputs": {...}}
Schema: https://tttkmbb.com/api/v1/calculators/dog-age · Markdown: https://tttkmbb.com/everyday/dog-age.md · JSON definition: https://tttkmbb.com/everyday/dog-age.json
MCP: server https://tttkmbb.com/mcp, tool run_calculator with calculator_id="dog-age"
OpenAPI operationId: convert_dog_age_to_human_years
Freshness: static. Authentication: none. Rate limit: fair use (see rate limits).

Sources

FAQ

Is one dog year really seven human years?

No. The 7:1 rule overstates puppy development and understates ageing in large breeds; a 1-year-old dog is already sexually mature, closer to a 15-year-old human.

Why does the epigenetic formula give such a high number for a young dog?

It tracks DNA methylation, which changes fastest early in life: a 1-year-old dog scores 31 and a 2-year-old 42, then the curve flattens so a 12-year-old scores about 71, close to the chart.

Related calculators

Cat Age Calculator — Same conversion for cats.
Pet Calorie Calculator — Daily calorie needs by weight and life stage.