Pet Life Stage Reference Chart
Life stage age ranges for cats and dogs, from published veterinary guidelines.
Cat life stages
Per the 2021 AAHA/AAFP Feline Life Stage Guidelines.
| Stage | Age range |
|---|---|
| Kitten | Birth – 1 year |
| Young adult | 1 – 6 years |
| Mature adult | 7 – 10 years |
| Senior | Over 10 years AAHA/AAFP note individual cats vary — a healthy 11-year-old may still be managed as a mature adult at a vet's discretion. |
| End of life | Any age The guidelines define this as a fifth, non-age-specific stage — a cat's physical decline near the end of life, not a birthday-based cutoff. |
Dog aging rate and senior onset by size
AAHA’s 2019 Canine Life Stage Guidelines define senior as roughly the last 25% of a dog’s estimated lifespan rather than a fixed age — AAHA deliberately does not publish exact ages for this stage. The onset ages below are this tool’s own approximation of what that lifespan-based rule works out to per size category, not AAHA’s own stated figures.
| Size | Adult weight | Senior onset | Aging rate after age 2 |
|---|---|---|---|
| Small | Up to 20 lb (9 kg) | ~10–12 years (approximate) | +4 human years / dog year |
| Medium | 21–50 lb (9.5–23 kg) | ~9–10 years (approximate) | +5 human years / dog year |
| Large | 51–100 lb (23–45 kg) | ~7–8 years (approximate) | +6 human years / dog year |
| Giant | Over 100 lb (45 kg) | ~5–6 years (approximate) | +7 human years / dog year |
Retrieved via web research and cited in this project’s lib/life-stage-reference.ts(see also docs/domain-reference.md for the full review and confidence notes) — approximate guidance, not an exact cutoff for any individual pet. Always consult your veterinarian for health assessments.
Frequently asked questions
- Why is there one cat table but a size-split dog table?
- Cats age fairly consistently across breeds, so veterinary guidelines use one life-stage table. Dogs vary enormously by adult size, and AAHA's own canine guidelines define senior as roughly the last 25% of a dog's estimated lifespan rather than a fixed age — since lifespan falls with size, that works out to giant breeds reaching senior status around 5–6 years and small breeds not until roughly 10–12, as an approximation, not the guideline's own stated cutoff.
- Are these exact cutoffs?
- No — for cats, the age ranges come directly from the AAHA/AAFP guidelines but are still described as approximate. For dogs, AAHA deliberately does not publish fixed ages for the mature-adult/senior stages at all (it says individual variation is too large), so the dog senior-onset ages here are this tool's own approximation of AAHA's lifespan-based rule, not a number AAHA itself states. A healthy pet at the edge of a range may be treated as the earlier stage at a vet's discretion.