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Dog Years Calculator

A 5-year-old medium dog is about 36 in human years; a 2020 DNA study puts it near 57. Dog aging is fast early then slows, and big dogs age quicker than small ones. Enter your dog's age and weight for a size-based number plus the DNA-based estimate.

By Sikander Malik · Updated October 10, 2026 · Sources

years
lb

Sets the size band: small, medium, large or giant.

About

36human years

DNA-based estimate (from a study of Labrador Retrievers): about 57 human years.

Size bandMedium (21–50 lb)
Life stageMature adult
Show the math
Size chart by age, with interpolation between years.
DNA formula: human = 16 × ln(dog age) + 31.

Estimates only, not veterinary advice. Ask your vet about your pet’s health.

How to use it

  1. Enter your dog's age in years.
  2. Enter the adult weight so we can set the size band (small ≤20 lb, medium 21–50, large 51–100, giant >100).
  3. Read the human-year age from the size chart, plus the DNA-based estimate.
Close-up portrait of a senior dog with a grey muzzle

Photo: Anderson / Pexels

The formula, with two examples

Method 1 is a size-based chart (AVMA-style): the first year counts for about 15 human years, the second adds about 9 more, and later years add 4 to 11 depending on size. We interpolate between whole years. Method 2 is the 2020 epigenetic formula human = 16 × ln(dog age) + 31, from DNA methylation in Labrador Retrievers, valid from age 1.

Example 1. A 5-year-old, 40 lb (medium) dog is 36 human years on the chart. The DNA formula gives 16 × ln 5 + 31 = 56.75, about 57.

Example 2. A 10-year-old, 75 lb (large) dog is 66 human years on the chart. The DNA formula gives 16 × ln 10 + 31 = 67.84, about 68.

What this calculator doesn’t cover

  • Individual health, which matters more than any formula.
  • Mixed-size dogs; use the adult weight to pick the band.
  • The “7 years” rule, which is wrong: it overstates early years and understates old age.
Dog age in human years, by size
Dog age (years)SmallMediumLargeGiant
115151512
224242422
328282831
432323238
536363645
640424549
744475056
848515564
952566171
1056606679
1160657286
1264697793
13687482100
14727888107
15768393114
16808799121
Source: AVMA size-based dog age chart. Small ≤20 lb, medium 21–50, large 51–100, giant >100 lb.

Tips

  • Use adult weight, not current puppy weight, to pick the size band.
  • Big dogs cross into “senior” earlier, often around 6 to 7 years, while small dogs may not until 9 or 10.
  • The DNA formula was built on Labradors, so treat it as a second opinion next to the size chart.

Questions owners ask

Is one dog year really 7 human years?
No. The 7-year rule is a rough average that gets both ends wrong. A dog’s first year is closer to 15 human years, and the pace then slows and depends on size. Our chart and the DNA formula both show this curve instead of a flat multiplier.
How old is a 2-year-old dog in human years?
About 24 human years for most sizes. The first two years pack in the fastest aging: roughly 15 human years in year one and about 9 more in year two. After that, each dog year adds 4 to 11 human years depending on the dog’s size.
Why do big dogs age faster?
Large and giant breeds grow for longer and tend to have shorter lifespans, so they move through the aging curve more quickly. By 10 years a small dog is about 56 in human years, a large dog about 66, and a giant breed about 79 on the chart.
What is the new DNA formula?
In 2020, researchers compared DNA methylation in dogs and humans and produced human = 16 × ln(dog age) + 31. It fits the fast-early, slow-later pattern well and is valid from age 1. It was built mainly on Labrador Retrievers, so individual breeds vary.
At what age is a dog a senior?
It depends on size. Many large dogs are considered senior around 6 to 7 years, while small dogs often reach that stage closer to 9 or 10. Senior care is usually framed as the last quarter of a dog’s expected lifespan, which is shorter for bigger breeds.
Do dog years work for puppies?
Under a year, aging is extremely fast, so a single number is rough. The chart interpolates from birth to the one-year value (15 human years for most sizes, 12 for giants). The DNA formula only becomes meaningful at age 1 and above.

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Sources

Estimates only, not veterinary advice. Ask your vet about your pet’s health.