Dog years to human years chart
| Dog age | Small up to 20 lb | Medium 21–50 lb | Large 51–100 lb | Giant over 100 lb |
|---|---|---|---|---|
| 1 year | 15 | 15 | 15 | 12 |
| 2 years | 24 | 24 | 24 | 22 |
| 3 years | 28 | 28 | 28 | 31 |
| 4 years | 32 | 32 | 32 | 38 |
| 5 years | 36 | 36 | 36 | 45 |
| 6 years | 40 | 42 | 45 | 49 |
| 7 years | 44 | 47 | 50 | 56 |
| 8 years | 48 | 51 | 55 | 64 |
| 9 years | 52 | 56 | 61 | 71 |
| 10 years | 56 | 60 | 66 | 78 |
| 11 years | 60 | 65 | 72 | 86 |
| 12 years | 64 | 69 | 77 | 93 |
| 13 years | 68 | 74 | 82 | 101 |
| 14 years | 72 | 78 | 88 | 108 |
| 15 years | 76 | 83 | 93 | 115 |
| 16 years | 80 | 87 | 99 | 123 |
| 18 years | 88 | 96 | 110 | – |
| 20 years | 96 | 105 | – | – |
Ages in human years. Ages above 16 extend the chart's yearly steps; few large and giant dogs live that long.
How to calculate dog years
The old "multiply by seven" rule is a myth. Dogs mature very quickly: by their first birthday most dogs are about as developed as a 15-year-old person, and by two they are like a person in their mid-twenties. After that, aging slows down to about 4 to 9 human years per dog year.
The American Veterinary Medical Association sums it up as 15 human years for the first year, 9 for the second, and about 5 for each year after that. Size matters because large and giant breeds age faster in later life, which is why the chart splits into four columns from age six onward.
The DNA-based formula
In 2020, researchers at the University of California San Diego compared changes in DNA (methylation) of Labrador Retrievers and people and proposed a new formula:
human age = 16 × ln(dog age) + 31
It says a one-year-old dog is like a 31-year-old person in molecular terms, and that aging slows strongly later on. The study looked at one breed only, so most vets still use the size-based chart. The calculator shows both.
Dog life stages
- Puppy: birth to about 1 year (up to 18–24 months in giant breeds).
- Young adult: until about 3 years.
- Mature adult: from about 3 years until the last quarter of expected lifespan.
- Senior: the last quarter of expected lifespan, around 10 years for small dogs, 8 to 9 for medium and large dogs and 6 for giant breeds.
Senior dogs benefit from vet check-ups every six months, because problems like kidney disease, arthritis or dental disease are easier to treat when caught early. Older dogs often need fewer calories; our dog food calculator has a senior setting.
Frequently asked questions
Is one dog year really seven human years?
No. Dogs age much faster early on: a one-year-old dog is roughly like a 15-year-old person, and a two-year-old like a 24-year-old. After that, each dog year counts as about 4 to 9 human years, depending on size. Large and giant breeds age faster than small ones.
How old is a 10-year-old dog in human years?
About 56 for a small dog, 60 for a medium dog, 66 for a large dog and 78 for a giant breed.
Why do big dogs age faster?
Large and giant breeds grow very fast and have shorter average lifespans. Researchers think rapid growth is linked to faster aging, though the exact reasons are still being studied.
When is a dog a senior?
Vets usually consider a dog senior in the last quarter of its expected lifespan. That is around 10 years for small dogs, 8 to 9 for medium and large dogs and as early as 6 for giant breeds.
Sources
- American Veterinary Medical Association (AVMA): senior pet care and aging.
- Wang T, Ma J, Hogan AN, et al. Quantitative translation of dog-to-human aging by conserved remodeling of the DNA methylome. Cell Systems, 2020.
- AAHA Canine Life Stage Guidelines, 2019.
Human-year equivalents are approximations for general information, not veterinary advice. Last updated: October 2026.