# What is my cat’s age in human years?

Converts a cat’s age, from its birthday or in years and months, to human-equivalent years on the AAHA/AAFP feline age chart, and names its life stage.

- Page: https://www.acalculator.org/days/cat-age-calculator
- JSON spec: https://www.acalculator.org/days/cat-age-calculator.json
- Version: f1284abeb8cf

## Default answer

Example with the default inputs (What do you know? Birthday, Cat’s birthday October 2, 2021, Age on October 2, 2026) on the example date Friday, October 2, 2026: A cat of 5 years is about 36 in human years (Young adult).

## Inputs

| Key | Label | Description |
| --- | --- | --- |
| known | What do you know? | Whether you know the cat’s birthday or its age in years and months. |
| birth | Cat’s birthday | The day the cat was born, or your best guess. |
| on | Age on | The date to work out the age on. Today, unless you change it. |
| years | Years | The cat’s age in whole years. |
| months | Months | Months past the whole years, 0 to 11. |

## Outputs

| Key | Label | Description |
| --- | --- | --- |
| human | In human years | The human-equivalent age on the AAHA/AAFP chart, read on a straight line between its points. |
| stage | Life stage | The AAHA/AAFP 2021 life stage: kitten, young adult, mature adult, or senior. |
| age | Cat’s age | The cat’s age in whole years and months. |
| totalMonths | Age in months | The cat’s age in whole months. |

## Method

human years on straight lines through (0 months, 0), (3, 4), (6, 10), (12, 15), (18, 21), (24, 24); from 24 months, human years = 24 + 4 × (cat years − 2).

## Assumptions

- The chart is the AAHA/AAFP and International Cat Care feline age chart: 3 months = 4, 6 months = 10, 12 months = 15, 18 months = 21, 2 years = 24, then 4 human years for each cat year.
- Between the chart’s points, the human age is read on a straight line, by whole months.
- A birthday counts completed months up to the age-on date; days past the last whole month are not counted.
- Life stages follow the 2021 AAHA/AAFP guidelines by completed years: kitten under 1, young adult 1 to 6, mature adult 7 to 10, senior over 10.
- The chart is an average for all cats; it does not depend on breed or size.

## Worked examples

1. known = age, years = 2, months = 0 gives human = 24, stage = Young adult, totalMonths = 24. Source: AAHA/AAFP and International Cat Care feline age chart, as printed by IAMS (https://www.iams.com/cat/cat-articles/calculating-your-pets-age-cat-years, retrieved 2026-10-01): 2 years = 24 human years; 2021 AAHA/AAFP Feline Life Stage Guidelines (https://catvets.com/resource/aaha-aafp-feline-life-stage-guidelines/): young adult 1 to 6 years.
2. known = age, years = 10, months = 0 gives human = 56, stage = Mature adult. Source: AAHA/AAFP and International Cat Care feline age chart, as printed by IAMS (https://www.iams.com/cat/cat-articles/calculating-your-pets-age-cat-years): 7 to 10 years = 44 to 56.
3. known = age, years = 0, months = 9 gives human = 12.5, stage = Kitten. Source: AAHA/AAFP and International Cat Care feline age chart, as printed by IAMS (https://www.iams.com/cat/cat-articles/calculating-your-pets-age-cat-years): 6 months = 10, 12 months = 15.
4. known = birth, birth = 2011-03-15, on = 2026-09-30 gives human = 78, stage = Senior, age = {"years":15,"months":6}, totalMonths = 186. Source: AAHA/AAFP and International Cat Care feline age chart, as printed by IAMS (https://www.iams.com/cat/cat-articles/calculating-your-pets-age-cat-years): 15 years = 76.

## FAQ

### How do I convert cat years to human years?

The first year of a cat’s life equals about 15 human years, the second adds 9 more (24 at age 2), and each year after that adds about 4. A 10-year-old cat is about 24 + 4 × 8 = 56 in human years.

### Is one cat year equal to seven human years?

No. Cats grow up fast: a 1-year-old cat is closer to a 15-year-old person. After age 2 the pace slows to about 4 human years per cat year, so the seven-year rule is wrong at both ends.

### What are the life stages of a cat?

The 2021 AAHA/AAFP Feline Life Stage Guidelines use kitten (birth up to 1 year), young adult (1 to 6 years), mature adult (7 to 10 years) and senior (over 10 years), plus end of life, which can come at any age.

### When is a cat a senior?

After age 10, by the 2021 AAHA/AAFP guidelines. That is about 60 in human years. Vets suggest more frequent check-ups from this age.

### How old is a 6-month-old kitten in human years?

About 10. The chart puts 3 months at about 4, 6 months at about 10 and 12 months at about 15 human years.

### Does breed change a cat’s age in human years?

The chart does not use breed or size; it is an average for all cats. Unlike dogs, cats vary little in size, so one chart is the usual rule.

### What if I do not know my cat’s birthday?

Choose Age and type your best guess in years and months. A vet can estimate a cat’s age from its teeth, eyes and coat.

## Sources

- American Animal Hospital Association and American Association of Feline Practitioners, 2021 AAHA/AAFP Feline Life Stage Guidelines, life stage definitions, retrieved 2026-10-01. https://catvets.com/resource/aaha-aafp-feline-life-stage-guidelines/
- Quimby J, et al. 2021 AAHA/AAFP Feline Life Stage Guidelines. Journal of Feline Medicine and Surgery, 2021, 23(3): 211–233, Table 1 (life stages), retrieved 2026-10-01. https://pmc.ncbi.nlm.nih.gov/articles/PMC10812130/
- IAMS, Cat age chart (from the guidelines of AAHA, AAFP and International Cat Care), retrieved 2026-10-01. https://www.iams.com/cat/cat-articles/calculating-your-pets-age-cat-years