Dog Age Calculator — Human Years by Breed Size

Convert your dog's age to human years using the AVMA breed-size method or the UCSD epigenetic DNA formula. More accurate than the outdated x7 rule.

July 2, 2026

Method

Dog's Age (years)

Breed Size

Human-Year Equivalent

39 years old

Medium (21–50 lb) · 5 dog years

Breed-size method: 15 human years for year one, +9 for year two, then a size-specific rate per year after (small +4, medium +5, large +6, giant +7) — based on the AVMA's published medium-breed example, adjusted for typical size-based aging variation. Epigenetic method: human age = 16 × ln(dog age) + 31, from a 2020 UC San Diego DNA methylation study — note this formula was derived from Labrador Retrievers only and doesn't adjust for breed size. Neither method is an exact substitute for veterinary assessment of your individual dog's health.

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Reference Values

Last verified: Jul 2, 2026

Category	Range	What It Means	Status
Small Breed (under 20 lb) ★	+4 human years per dog year after age 2	Slowest-aging category after maturity — often not considered senior until age 10, and typically lives longest overall.	★ Best
Medium Breed (21–50 lb)	+5 human years per dog year after age 2	The AVMA's own published example uses this category: 15 years for year one, 9 more for year two, then roughly 5 per year after.	Good
Large Breed (51–90 lb)	+6 human years per dog year after age 2	Reaches physical maturity a bit later than smaller breeds but ages faster afterward.	Okay
Giant Breed (over 90 lb)	+7 human years per dog year after age 2	Fastest-aging category — often considered senior by age 5–6, with a shorter typical lifespan than smaller breeds.	Poor

Source: AVMA published medium-breed example (15 + 9 + 5/year); breed-size aging-rate variation aggregated from veterinary and pet-health reporting. UC San Diego epigenetic (DNA methylation) formula: human age = 16 × ln(dog age) + 31 (Wang et al., Cell Systems, 2020 — derived from Labrador Retrievers only)

Worked Examples

Medium Breed, 5 Years Old (Breed-Size Method)

Method: Breed-Size (AVMA-based)
Size: Medium
Dog Age: 5 years

39 human years

Year 1 = 15, Year 2 = +9 (24 total), then +5/year for 3 more years: 24 + (5-2)×5 = 39.

Small Breed, 10 Years Old (Breed-Size Method)

Method: Breed-Size (AVMA-based)
Size: Small
Dog Age: 10 years

56 human years

24 + (10-2)×4 = 56. Small breeds age slower after year 2, so the same 10 dog-years results in a younger human-year equivalent than a larger breed.

Giant Breed, 6 Years Old (Breed-Size Method)

Method: Breed-Size (AVMA-based)
Size: Giant
Dog Age: 6 years

52 human years

24 + (6-2)×7 = 52. Giant breeds age fastest after maturity — often considered senior by this age.

Any Size, 10 Years Old (UCSD Epigenetic Formula)

Method: UCSD Epigenetic (DNA methylation)
Dog Age: 10 years

≈67.8 human years

16 × ln(10) + 31 = 67.8. This formula is breed-agnostic and was derived from DNA methylation data in Labrador Retrievers — it doesn't adjust for breed size the way the AVMA-based method does.

How to Use This Calculator

1

Choose your calculation method

Breed-size (adjusts for small/medium/large/giant) or UCSD epigenetic (DNA-based, breed-agnostic).
2

Enter your dog's age

In years — decimals are fine for puppies under 1 year old (e.g. 0.5 for 6 months).
3

Select breed size (if using breed-size method)

Choose based on your dog's adult weight: small (under 20 lb), medium (21–50 lb), large (51–90 lb), or giant (over 90 lb).
4

Read the human-year equivalent

Results show the estimated human-age equivalent based on your selected method.

What Each Value Means

Breed-Size Human-Year Equivalent (human years): Estimated human age using a piecewise formula: 15 years for the dog's first year, +9 for the second, then a size-specific rate per year after (4/5/6/7 for small/medium/large/giant), reflecting that dogs mature rapidly early in life and that aging rate afterward varies meaningfully by adult size.
Epigenetic Human-Year Equivalent (human years): Estimated human age using the formula 16 × ln(dog age) + 31, derived from comparing DNA methylation patterns (age-related chemical changes to DNA) in Labrador Retrievers against those in humans, published by UC San Diego researchers in 2020.

Frequently Asked Questions

Why is the 'multiply by 7' rule for dog years wrong?

The x7 rule assumes a constant aging ratio throughout a dog's life, but dogs actually mature extremely fast in year one (roughly equivalent to 15 human years) and year two (another 9 years, totaling 24), then age at a much slower, steadier rate afterward. It also ignores breed size entirely, even though small and giant breeds age at meaningfully different rates once past puberty. Veterinary organizations like the AVMA have moved away from recommending it.

How do you calculate dog age in human years using the breed-size method?

Year one of a dog's life equals about 15 human years. Year two adds about 9 more (24 total). Every year after that adds a size-specific amount: roughly 4 years for small breeds, 5 for medium, 6 for large, and 7 for giant breeds. For example, a 5-year-old medium dog: 24 + (5−2) × 5 = 39 human years.

What is the UCSD epigenetic dog age formula?

Human age = 16 × ln(dog age) + 31, developed by UC San Diego researchers in 2020 using DNA methylation patterns (chemical changes to DNA that accumulate with age) compared between dogs and humans. It's more scientifically grounded than either the x7 rule or the size-based method, but the underlying study used only Labrador Retrievers, so it doesn't account for breed-size differences in aging.

Which dog age calculation method is more accurate?

Neither is definitively 'more correct' — they measure different things. The breed-size method is a practical, widely-used approximation that accounts for size but is based on general veterinary observation rather than biological measurement. The epigenetic formula is grounded in actual DNA aging markers but was derived from a single breed and a single, relatively small study, so it doesn't generalize breed-size effects. For a general sense of your dog's life stage, either is a reasonable estimate — for anything health-related, your veterinarian's assessment of your individual dog matters far more than either formula.

At what age is a dog considered a senior?

It depends heavily on size: giant breeds are often considered senior by 5–6 years old, large breeds around 6–7, medium breeds around 7, and small breeds may not be considered senior until 10 years old or later. This variation is a direct result of the same size-based aging-rate difference this calculator models — giant breeds simply age faster after physical maturity than small breeds do.