Free tool
Pet age calculator
How old is your dog or cat in human years? Not seven times their age — that rule was never based on biology. This uses the multi-stage model behind the veterinary life stage guidelines, which front-loads the first two years and then slows down at a rate that depends on your dog's size.
The number is the fun part. The life stage underneath it is the part that changes what your pet actually needs.
A medium dog aged 3 years is roughly
29 human years
Life stage: Young adult
From the end of rapid growth to full physical and social maturity, reached by most dogs at 3 to 4 years.
What tends to change at this stage
Annual boosters, year-round parasite prevention, adult weight settling, and the start of dental care.
General information, not veterinary advice — worth raising at your next appointment.
A second opinion: the 2020 epigenetic clock, built from DNA methylation in Labrador Retrievers, puts the same dog at about 49 human years. It disagrees most in the early years, where it ages dogs faster than the chart does. It was derived from one breed, so treat it as an interesting cross-check rather than a better answer.
A medium dog typically lives 12–14 years, so the senior stage starts around 10.
Want the dates, not the arithmetic? Household Pet keeps your dog's date of birth, weight history and vaccination record in one place, and reminds the right person when the next thing is due.
Get the free appHow the conversion works
Both dogs and cats pack an extraordinary amount of development into their first two years, then settle into a slower, steadier rate. The model used here reflects that shape:
- Year one is worth about 15 human years.
- Year two adds about 9 more, so a two-year-old is roughly 24.
- Every year after that adds 4 human years for a cat or a small dog, 5 for a medium dog, 6 for a large one and 7 for a giant breed.
That last line is why a dog age chart with no size input is wrong for most dogs. A 10-year-old Cavoodle and a 10-year-old Great Dane are not remotely the same age.
Dog age chart, by size
How fast a dog ages after their second birthday depends on how big they grow. Find the band your dog lands in — the rate, the typical lifespan and the point they are considered senior all move with it.
| Size | Adult weight | Human years per year (after 2) | Typical lifespan | Senior from |
|---|---|---|---|---|
| Small | under 9 kg | +4 | 14–16 yrs | ~11 yrs |
| Medium | 9–23 kg | +5 | 12–14 yrs | ~10 yrs |
| Large | 23–45 kg | +6 | 10–12 yrs | ~8 yrs |
| Giant | over 45 kg | +7 | 8–10 yrs | ~7 yrs |
Senior is derived, not decreed: the canine guidelines define it as the last quarter of expected lifespan, so it moves with the size band rather than sitting at a fixed birthday.
Cat age chart
Cats are simpler: size does not meaningfully change the maths for domestic cats, so there is one curve. The feline life stage guidelines set the bands below, and senior starts at a fixed 11 rather than sliding with body size the way it does for dogs.
| Cat's age | Human years | Life stage |
|---|---|---|
| 6 months | 8 | Kitten |
| 1 year | 15 | Young adult |
| 2 years | 24 | Young adult |
| 3 years | 28 | Young adult |
| 5 years | 36 | Young adult |
| 7 years | 44 | Mature adult |
| 10 years | 56 | Mature adult |
| 11 years | 60 | Senior |
| 12 years | 64 | Senior |
| 15 years | 76 | Senior |
| 18 years | 88 | Senior |
| 20 years | 96 | Senior |
There is no feline equivalent of the epigenetic clock below — that research was done on dogs, so the calculator only offers the second opinion for dogs.
Why life stage matters more than the number
The veterinary guidelines are blunt about this. The canine task force notes that rather than attempting to calculate age equivalents to humans, life stage should be defined by age and characteristics — because that is what determines the care a pet needs. The feline guidelines take the same line, which is why they publish age bands for kitten, young adult, mature adult and senior rather than a conversion factor.
In practice, the transition that matters most is into the senior stage, when the recommendation typically shifts from annual to six-monthly check-ups and when a written history — weight trend, medications, what changed and when — starts earning its keep at every appointment.
Why there is no rabbit or ferret setting
Because we would have to make the numbers up. Dogs and cats have published life-stage guidelines behind them; rabbits, ferrets, birds and reptiles have nothing comparable, and a confident-looking figure with no source is worse than an honest gap. Household Pet still keeps records and reminders for those species — it just will not invent a human-age equivalent for them.
Common questions
- Is one dog year really seven human years?
- No. The "multiply by seven" rule is a rough average that was never based on biology, and it is wrong at both ends. A one-year-old dog is closer to a 15-year-old human, because the first year covers an enormous amount of development. After the second year the curve flattens, and how fast it flattens depends on the dog's size — a small dog adds roughly 4 human years per year, a giant breed roughly 7.
- Why does size change a dog's age in human years?
- Larger dogs have shorter lifespans, so each calendar year represents a larger share of their life. A Great Dane is a senior at around 7; a small terrier may not be until 11. This is why the calculator asks for adult size before it answers, and why a single dog-age chart with no size input will always be wrong for most dogs.
- How do you work out a cat's age in human years?
- The feline life stage guidelines put the first year at about 15 human years and the second at about 24 in total, then add roughly 4 human years for each year after that. Unlike dogs, size does not meaningfully change the calculation for domestic cats.
- When is my pet considered senior?
- For cats, the guidelines set senior at 11 years and over. For dogs it depends on size, because senior is defined as the last quarter of expected lifespan: roughly 11 years for a small dog, 10 for a medium, 8 for a large and 7 for a giant breed. Reaching that stage usually means moving from annual to six-monthly check-ups.
- Can you calculate age in human years for rabbits, ferrets or birds?
- Not honestly. There is no published veterinary conversion for those species comparable to the canine and feline life-stage guidelines, so any number would be invented. Household Pet still tracks records and reminders for rabbits, ferrets, birds, reptiles, horses and cattle — it just will not make up a human-age figure for them.
Next, the useful stuff
- Vaccination schedule generator — the first year as dates rather than ages, for a puppy or a kitten.
- Puppy vaccination schedule (Australia) — what is due when, in the first year.
- Paralysis tick season checklist — the seasonal risk that catches out new owners on the east coast.
- What pet insurance costs in Australia — premiums rise sharply with age, which is worth knowing before the senior stage.
- The Household Pet guide — how the health log, reminders and vet reports fit together.
- Get Household Pet free — one shared record per pet, with reminders that arrive on time.
Life stage is the part that changes their care
Knowing your pet has tipped into senior is useful once. Acting on it is ongoing — check-ups more often, weight watched more closely, medication that has to land on time. Household Pet keeps the whole health record in one place, shared with your household, and reminds you when something is due.
Sources
- 2019 AAHA Canine Life Stage Guidelines
- 2021 AAHA/AAFP Feline Life Stage Guidelines
- Wang et al., Cell Systems (2020) — dog-to-human aging by DNA methylation
This calculator is general information, not veterinary advice. Age conversion is an approximation and individual animals vary widely with breed, health and history — for anything specific to your pet, ask your registered veterinarian.