WiseCalcs

Dog years calculator

Enter your dog's age and pick its size. The calculator converts the age into human years using the modern method, where the first two years count for more and larger dogs age faster after that.

Use it to see your dog's age in human-equivalent years, adjusted for its size.

years

Human age

39 years

Each further year adds
5 years

The result updates as you type. The headline is the human-equivalent age; the second figure shows how many human years each further year now adds.

How does it work?

The first year counts as 15 human years and the second adds 9 (24 by age two). After that, larger dogs age faster, so the per-year rate rises with size.

Dog years formula

H=24+(age−2)×k(age>2)H = 24 + (\text{age} - 2)\times k \quad (\text{age} > 2)
H
Human-equivalent age in years.
age
The dog's age in years.
k
Human years per dog year after 2: 4 small, 5 medium, 6 large.

A 5-year-old medium dog: 24 + (5 − 2) × 5 = 39 human years.

Method & sources

The first year counts as 15 human years and the second adds 9 (24 by age two). After age two, each dog year adds 4 (small), 5 (medium), or 6 (large) human years. Size bands are a guide; breed and individual health vary.

Sources

Where this method comes from — use these references to understand the formula, assumptions, and limits.

How we calculate

  • The first year counts as 15 human years and the second adds 9 (24 by age two).
  • After age two, each dog year adds 4 (small), 5 (medium), or 6 (large) human years.
  • Size bands are a guide; breed and individual health vary.

Rounding

Ages are shown to one decimal. The calculation uses full precision.

What this calculator does

The old rule of multiplying by seven is too simple. Dogs mature fast early on, then age at a rate that depends on size. This calculator counts the first year as 15 human years, the second as 9 more, and each year after that by a size-based amount.

How to use it

  1. Enter your dog's age in years.
  2. Pick a size band: small, medium, or large.
  3. Read the human-equivalent age.
  4. Check how fast each future year now counts.

A worked example

A 5-year-old medium dog is 24 + (5 − 2) × 5 = 39 human years. A large dog the same age would be 42, because larger breeds age a little faster.

Why size matters

Small breeds tend to live longer and age more slowly in later life, while large breeds age faster. The size band adjusts the per-year rate after the first two formative years.

Common mistakes

  • Using the flat 'times seven' rule, which overstates young dogs.
  • Picking the wrong size band for the breed.
  • Expecting exactness — individual dogs vary with health and breed.

When it's useful

For fun, for understanding a dog's life stage, or for thinking about age-appropriate care as your dog gets older.

FAQ

Is the 'multiply by seven' rule accurate?
No. Dogs age much faster in their first two years and then at a rate that depends on size, so a flat multiplier is misleading.
How does size change the result?
After age two, each year adds 4 human years for small dogs, 5 for medium, and 6 for large, reflecting how larger breeds age faster.
Which size band should I pick?
Roughly: small under 10 kg, medium 10–25 kg, large over 25 kg. Use your dog's adult weight as a guide.
How old is a 1-year-old dog?
About 15 human years. Dogs reach the equivalent of adolescence well before their first birthday.
Does breed matter beyond size?
Yes, somewhat. Lifespan varies by breed, but size is the main driver of ageing rate, so this method uses size bands.
Can I share a calculation?
Yes. Use Share to copy a link that reopens the calculator with the same age and size.

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<iframe src="https://wisecalcs.com/embed/en/dog-years-calculator" width="100%" height="520" style="border:0" loading="lazy"></iframe> <p>Calculator from <a href="https://wisecalcs.com/en/pets/dog-years-calculator">WiseCalcs</a></p>