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Cat Age Calculator

Converts a cat's age to human-equivalent years with the veterinary convention used by International Cat Care and the AAHA/AAFP chart (first year 15, second year 9, then 4 per year) and assigns the International Cat Care life stage (kitten, junior, adult, mature, senior, super senior).

When to use

You want a cat's age in human years or its life stage for feeding, vaccination or health-check planning.

Do not use when: The animal is a dog (use dog-age, which adjusts for breed size) or you need calorie needs (use pet-calories).

Formula

age ≤ 0.5: 20·age; 0.5–1: 10 + 10·(age − 0.5); 1–2: 15 + 9·(age − 1); age > 2: 24 + 4·(age − 2)

The convention approximates feline maturation: a 1-year-old cat is roughly a 15-year-old human and a 2-year-old about 24; after that each cat year adds about four human years. Individual cats vary with genetics, diet and indoor/outdoor life.

Inputs

Parameter	Type	Unit	Required	Description
`cat_age_years`	number	years	yes	Age of the cat in years (e.g. 0.5 for six months). Range: ≥ 0.1, ≤ 40

Outputs

Output	Type	Unit	Description
`human_years`	number	years	Human years by the 15 / 9 / 4-per-year convention (six months ≈ 10).
`life_stage`	string		International Cat Care stage: kitten (0–6 months), junior (7 months–2 years), adult (3–6), mature (7–10), senior (11–14), super senior (15+).
`next_stage`	string		The following life stage and the cat age at which it begins.

Example

5-year-old cat: {"cat_age_years":5} → {"human_years":36,"life_stage":"Adult","next_stage":"Mature from 7 years"}

12-year-old cat: {"cat_age_years":12} → {"human_years":64,"life_stage":"Senior","next_stage":"Super senior from 15 years"}

GET https://tttkmbb.com/api/v1/calculate/cat-age?cat_age_years=5

Machine access

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

Sources

FAQ

When is a cat considered senior?

International Cat Care uses 11 years (super senior from 15); the AAHA/AAFP guidelines start the senior stage at 10. Many vets recommend twice-yearly check-ups from about 10 years.

Do indoor and outdoor cats age differently?

The conversion is the same, but outdoor cats face more injury and disease, so their life expectancy is shorter on average.

Related calculators

Dog Age Calculator — Same conversion for dogs, adjusted for size.
Pet Calorie Calculator — Daily calorie needs for cats by weight and life stage.