Dog Age Calculator: Dog and Cat Years to Human Years

Dog and cat age in human years: size-based chart

The tool counts 15 human years for the pet's first year, 9 for the second, then a fixed number per year depending on size: 4 for a cat or small dog, 5 for a medium dog, 6.5 for a large dog and 8 for a giant breed. A medium dog aged four and a half is therefore about 37 in human years.

Chart applied

• From 0 to 1 year: age × 15.
• From 1 to 2 years: 15 + (age − 1) × 9.
• After 2 years: 24 + (age − 2) × yearly rate.

Yearly rate: cat 4; small dog (under 10 kg) 4; medium (10-23 kg) 5; large (23-40 kg) 6.5; giant (over 40 kg) 8. The result is rounded to the nearest year. The life stage follows actual age before 3 (puppy or kitten under 1, young adult from 1 to 3), then the human equivalent: senior from 50, geriatric from 70.

Examples

Medium dog aged 4 years 6 months: 24 + 2.5 × 5 = 36.5, rounded to 37, adult stage. At 8 years a small dog is 48 in human years, a medium dog 54, a large dog 63 and a giant 72 (geriatric). A 10-year-old cat equals 24 + 8 × 4 = 56.

What the chart does not tell you

The "one dog year equals seven human years" rule has no scientific basis, and the tool's chart remains an approximation based on common veterinary practice, with no primary source verified. Another approach exists: the study by Wang et al. (Cell Systems, 2020), based on DNA methylation in Labradors, proposes human age = 16 × ln(dog age) + 31. It gives 31 years at age 1, 55 at four and a half and about 70 at 12; it was built on a single breed and the tool does not use it. The result is indicative and does not replace a vet's opinion.

Sources and dates: National Human Genome Research Institute press release of 9 July 2020 on the Wang et al. study (NHGRI, Researchers reframe dog-to-human aging comparisons); 15/9 then 4-8 years per year chart: indicative value, not verified (checked on 14/10/2026)

Frequently Asked Questions

Is one dog year really seven human years?

No, that rule oversimplifies. Dogs age fast at first: the tool counts 15 human years for the first year and 9 for the second, then 4 to 8 years per year depending on size. A medium dog aged 2 is therefore about 24 in human years, not 14.

Why do large dogs age faster?

Large breeds have a shorter life expectancy than small ones. The tool reflects this after age 2: 4 human years per year for a small dog, 5 for a medium one, 6.5 for a large one and 8 for a giant. At 8 that gives 48 for a Chihuahua against 72 for a Great Dane.

How old is a 10-year-old cat in human years?

With the tool's chart (15 years for the first year, 9 for the second, then 4 per year), a 10-year-old cat equals 56 human years. It then falls in the tool's senior stage, which starts at a human equivalent of 50.

What is the epigenetic dog age formula?

A 2020 study by Wang et al. in Cell Systems, based on DNA methylation in Labradors, proposes human age = 16 × ln(dog age) + 31. A 1-year-old dog would be 31 in human years and a 12-year-old about 70. It was built on one breed only and the tool does not use it.

Is this tool really free?

Yes, all tools on Kristools are 100% free and accessible without registration.

Is my data protected?

Yes. All processing is performed directly and securely inside your browser. No personal data is sent to our servers.