Skip to calculator

Pets · Dogs

Convert a dog’s age into human years

Age and size. The tool applies a stepped chart, not the “times seven” rule.

Calculate

In years; decimals are allowed (1.5 = a year and a half).

How the calculator works

The rule “one dog year equals seven human years” is wrong: the first two years count more, and the pace after that depends on size. Here: 15 years for the first year, 9 for the second, then 4 (small), 5 (medium), or 6 (large) per year. A 5-year medium dog is 15+9+15 = 39. That is neither a life expectancy nor a diagnosis.

Formula and method

1 year → 15

First year, every size.

2 years → 24

15 + 9.

n>2 → 24 + (n−2) × k

k = 4, 5, or 6 by size.

A teaching chart widely reused in pet media, not a single clinical paper. Large dogs often age faster after two years, hence a higher k. No breed is singled out.

Worked example

5-year medium dog

age = 5, size = medium.

  1. 15 + 9 = 24 for the first two years.
  2. 3 × 5 = 15 after that.
  3. 24 + 15 = 39.

39 human years (chart).

Input notes

Dog’s age
Current age in years. 0.5 = six months.
Size
Approximate adult size, not the puppy’s weight.

Assumptions and limits

Assumptions

  • 15 / 9 / 4–6 chart.
  • Adult size, not breed.
  • An honest age entry.

Limits

  • No breed or disease.
  • No life expectancy.
  • Not a veterinary opinion.

How to read the result

A “human age” is a way to talk about life pace, not a way to dose a drug. The veterinarian relies on the exam, not this number.

Common mistakes

  • Multiplying by 7.

    The first two years weigh more than the years after.

  • Picking “large” for a puppy that will grow.

    Use the expected adult size.

  • Reading a life expectancy.

    The chart does not say when a dog will die.

Methodology · Sources

Related calculations

Frequently asked questions

Why not × 7?

Because the first two years count more.

A puppy “ages” faster in the first year. After that the pace depends on size.

Do small dogs live longer?

Often, on average.

The chart slows after two years for small dogs. That is not an individual guarantee.

Does this replace a vet visit?

No.

No vaccine, no pain, and no body weight enter the calculation.

Author and update

Written by Rédaction HexaCalc (editorial team). Content last updated: August 25, 2026. No third-party medical or financial review is claimed.

This calculation uses a standard mathematical identity. See also the methodology.

Have a cat too?

The feline chart uses 15, 9, then 4 human years per year.

Cat age

Category: Pets