Pet Age Calculator
How old is your dog or cat in human years?
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The 'one pet year equals seven human years' rule is wrong. Pets mature much faster in their first two years and then age more gradually — and larger dogs age faster still. Enter your pet's age, species, and (for dogs) size to get a realistic human-age figure.
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How Old Is My Pet in Human Years? — The Quick Answer
A pet's first year is roughly 15 human years, and the second adds about 9 more (so a 2-year-old is about 24). After that, add around 4–7 human years per pet year, with larger dogs ageing faster.
Shortcut
year 1 ≈ 15 · year 2 ≈ +9 (= 24) · each later year ≈ +4 to +7
Fact-Checking Claims You May Have Seen Online
Multiply your pet's age by 7 to get human years
False
The ×7 rule is a myth. Pets age very fast in year one (a 1-year-old dog is already ~15 in human terms), then slow down — so ×7 badly underestimates the early years and misstates the rest.
A big dog and a small dog of the same age are the same in human years
False
Large and giant breeds age faster. A 5-year-old small breed is 'younger' in human years than a 5-year-old giant breed, which is why the calculator asks for breed size.
Dog's age in human years (by size)
| Pet age | Small | Medium | Large | Giant |
|---|---|---|---|---|
| 1 year | 15 | 15 | 15 | 15 |
| 2 years | 24 | 24 | 24 | 24 |
| 5 years | 36 | 39 | 42 | 45 |
| 10 years | 56 | 64 | 72 | 80 |
Cats follow a similar early curve to medium dogs (15, then 24, then about +4 a year). These figures are well-established estimates from veterinary sources, not exact predictions for an individual animal.
How It Works
The Method
A curve, not a straight multiplication
Formula
1 year → 15 2 years → 24 + 4 to 7 human years per additional pet year (size-dependent for dogs)
Variables
The fast start
Pets reach physical maturity very quickly. By the end of the second year most are fully grown, which is why the second year adds about 9 human years — bringing a 2-year-old to roughly 24.
Size matters for dogs
After age two, each dog year adds about 4 human years for a small breed, rising to roughly 7 for a giant breed. Larger dogs live shorter lives and their bodies age faster, so the same calendar age means 'older' in human terms.
Note: These curves come from veterinary and breed organisations. They're population averages — an individual pet's health, diet, and genetics shift the real picture, so treat the result as a friendly estimate rather than a medical assessment.
Last updated: October 6, 2026
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Frequently Asked Questions
Is 'multiply by 7' a real way to calculate pet age?
No — it's a myth. The ×7 rule was a rough convenience and it's badly wrong at both ends: it underestimates the first year (a 1-year-old dog is about 15 in human years, not 7) and it misses how much breed size matters. A proper ageing curve gives a far more realistic figure.
How do I convert my dog's age to human years?
For a medium dog: the first year counts as about 15 human years, the second adds 9 (reaching 24), and each year after adds about 5. So a 10-year-old medium dog is roughly 24 + 5 × 8 = 64 in human years. Small breeds age slower and giant breeds faster.
Do cats age the same as dogs?
Cats follow a similar early curve to medium dogs — about 15 human years for the first year and 24 by the second — and then roughly 4 human years per cat year after that. Cats are less affected by size, so there's no size input for them here.
Why does dog size change the calculation?
Larger dogs age faster and have shorter average lifespans than smaller ones. A giant breed may be considered a senior at the same calendar age that a small breed is only middle-aged. The calculator accounts for this so the human-year estimate reflects the dog's likely life stage.