# 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.

- Calculator id: `dog-age` · Category: Everyday Life (`everyday`) · Tool name: `convert_dog_age_to_human_years`
- Canonical page: https://tttkmbb.com/everyday/dog-age · This document: https://tttkmbb.com/everyday/dog-age.md · JSON definition: https://tttkmbb.com/everyday/dog-age.json

## Purpose

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.

**Use when:** 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.

## Input

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

## Output

| Field | 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. |

## 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.

## Data Sources

- AAHA (2019) Canine and Feline Age Chart – physiological age in human years by size class — https://www.aaha.org/wp-content/uploads/globalassets/02-guidelines/canine-life-stage-2019/canine_and_feline_age_chart_poster.pdf (standard, retrieved 2026-09-24)
- AVMA – Senior pets: how a pet's age compares with a human's — https://www.avma.org/resources-tools/pet-owners/petcare/senior-pets (reference, retrieved 2026-09-24)
- Wang T et al. (2020) Quantitative Translation of Dog-to-Human Aging by Conserved Remodeling of the DNA Methylome, Cell Systems 11:176-185 — https://www.cell.com/cell-systems/fulltext/S2405-4712(20)30203-9 (peer_reviewed, retrieved 2026-09-24)

Data freshness: `static`. Deterministic formula with fixed constants; results never go stale. Inputs supplied by the caller determine the output.

## API

- `GET https://tttkmbb.com/api/v1/calculate/dog-age?dog_age_years=…`
- `POST https://tttkmbb.com/api/v1/calculate/dog-age` with JSON body `{"inputs": {…}}`
- Response: unified envelope (`success`, `request`, `result.values`, `result.units`, `sources`, `freshness`, `timestamp`, `next_actions`, `links`); see https://tttkmbb.com/docs/response-format.md
- Schema: https://tttkmbb.com/api/v1/calculators/dog-age · OpenAPI operationId `convert_dog_age_to_human_years` in https://tttkmbb.com/openapi.json
- Authentication: none. Rate limit: fair use, see https://tttkmbb.com/docs/rate-limits.md.

## MCP

- Server: `https://tttkmbb.com/mcp` (Streamable HTTP, JSON-RPC 2.0, no auth)
- Tool:  `run_calculator` with `{"calculator_id": "dog-age", "inputs": {…}}`

## Example

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

## Limitations

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. 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. All values are computed from the formula above; no measurement or live data is involved.

## 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

- [Cat Age Calculator](https://tttkmbb.com/everyday/cat-age.md) — Same conversion for cats.
- [Pet Calorie Calculator](https://tttkmbb.com/everyday/pet-calories.md) — Daily calorie needs by weight and life stage.