Donaldson R F Cat Age Calculator
Enter your cat’s age (or date of birth) to see a rough human-equivalent range and the veterinary life stage it falls in. Nothing leaves your browser.
Estimate, not veterinary advice.
The human-equivalent range comes from popular rules of thumb, not from research on your cat. Speak to your vet about health, behaviour and care.
-Age
-Human years (rough range)
-Life stage
-Share of a typical lifespan
More pets: all pet age calculators.
How this works
Estimate, not veterinary advice. For your animal’s health, behaviour, diet and care, speak to a vet. This page cannot diagnose anything, and no calculator can tell you how old an animal ‘feels’ or how long it will live.
Quick answer
A cat of 5 is roughly 35 to 40 in human terms. Cats are ‘adults’ from 1 year, ‘mature’ from 7 and ‘senior’ from about 11.
How the result is calculated, step by step
- The first year counts as 15 human years.
- The second year adds 9 more, so 2 years is 24.
- Every year after that adds 4.
- We then show the multiples of five that enclose the result, so you get a band instead of a falsely exact number.
Example: a cat of 5 years. 15 + 9 = 24 for the first two years, plus 3 more years × 4 = 12, so 36. The band shown is 35 to 40.
Where the numbers come from, and what they assume
- The 15 / 9 / 4 rule appears on many pet-care sites. In the three we read (International Cat Care, Purina UK and PetMD) none gives evidence for it, and Purina says outright that there is no reliable scientific way to compare human and cat years.
- The AAHA/AAFP guidelines were written to define life stages for care, and deliberately give no human-age equivalents.
- Cats do not age in a straight line, and a cat’s ‘human age’ is only a way of picturing where it is in life, not a medical measurement.
Why animal age and human age are not exact equivalents. Species age in different ways: growth, breeding age, illness and old age do not line up with ours year for year. A ‘human age’ is only a way of picturing where an animal is in its life. Two animals of the same age can be at very different stages of health.
How much you can trust each result
| Result | Confidence label | Based on |
|---|---|---|
| Human-equivalent range | Popular rule of thumb — rough idea only | Rules of thumb from International Cat Care: How to tell your cat’s age in human years (updated 28 November 2025), Purina UK: Cat years to human years, PetMD: Cat age chart, how old is my cat in human years |
| Life stage | Veterinary life-stage guideline | 2021 AAHA/AAFP Feline Life Stage Guidelines (Quimby J, Gowland S, Carney HC, et al.), J Feline Med Surg 2021;23(3):211–233 |
| Share of a typical lifespan | Popular rule of thumb — rough idea only | Typical lifespan: 12 to 18 years. Cats live on average around 12–14 years, and reaching the late teens or early twenties is not unusual. (International Cat Care: How to tell your cat’s age in human years (updated 28 November 2025)) Indoor cats 16 to 18 years and sometimes 20; outdoor cats about 13–14 years. (Purina UK: Cat years to human years) |
- Scientific formula: a formula fitted to research data that we read in the original paper.
- Peer-reviewed scientific article: a peer-reviewed article in the scientific or veterinary literature that we read, but not an official guideline issued by a veterinary or animal-welfare body.
- Veterinary life-stage guideline: stages or lifespans published by a veterinary body or animal-welfare organisation whose page we read.
- Popular rule of thumb — rough idea only: a rule that appears only in secondary sources (care websites, articles). We read at least two, show the result as a range, list what we read below, and found no primary scientific basis for it.
Limits
- Breed, indoor or outdoor life, weight, illness and genetics all change how a cat ages; the rule ignores all of them.
- Life-expectancy figures from different sources differ (12–14 years against 16–18 for indoor cats), which is why we show a range.
- Breed or type, size, health, genetics and environment all change how an animal ages. None of them is in the calculation.
- The maximum age this page accepts (40 years) is only a sanity check, not a claim about how long cats live.
Estimate, not veterinary advice. For your animal’s health, behaviour, diet and care, speak to a vet. This page cannot diagnose anything, and no calculator can tell you how old an animal ‘feels’ or how long it will live.
Sources and date checked
Everything below was opened and read on 27 September 2026. If a page has changed since, the numbers here may be out of date.
- International Cat Care: How to tell your cat’s age in human years (updated 28 November 2025) — what we read: Conversion table (first two years = 24 human years, then 4 per year), life-stage table and the statement that cats live 12–14 years on average. The page does not name a scientific basis. (checked 27 September 2026)
- Purina UK: Cat years to human years — what we read: Conversion rule (15, then 9, then 4 per year) and lifespans. The page itself says there is no reliable scientific way to compare human and cat years. (checked 27 September 2026)
- PetMD: Cat age chart, how old is my cat in human years — what we read: The same 15 / 24 / 4-per-year rule, which the article attributes to the American Veterinary Medical Association. We did not read the AVMA material. (checked 27 September 2026)
- 2021 AAHA/AAFP Feline Life Stage Guidelines (Quimby J, Gowland S, Carney HC, et al.), J Feline Med Surg 2021;23(3):211–233 — what we read: Table 1 (life stages by age). The guidelines give no human-age equivalents. (checked 27 September 2026)
Other pets: dog, cat, horse, rabbit, guinea pig, hamster, budgerigar, cockatiel, tortoise and turtle. For dates and people, try the Age Calculator.