Dog Age Calculator
Convert your dog’s age to human years, adjusted for size, with two methods side by side.
Small: 20 lb or less · Medium: 21–50 lb · Large: 51–90 lb · Giant: over 90 lb
In human years
Vet size chart
47
UCSD formula
62
- Life stage
- Mature adult
- Dog’s age
- 7 years
Chart: AAHA-published size chart. Formula: 16 × ln(7.00) + 31 = 62.1.
Quick answer
A dog’s first year equals about 15 human years and the second about 24. After that, add about 4 years per year for small dogs and up to 7 or more for giant breeds. A 7-year-old medium dog is about 47 on the vet chart, and about 62 on the UC San Diego formula.
How do I use the dog age calculator?
- Enter your dog’s age in years and months. For a rescue with an unknown birthday, use your vet’s estimate.
- Pick the size by adult weight: small (20 lb or less), medium (21–50 lb), large (51–90 lb) or giant (over 90 lb).
- Read both results. The size chart is the one most vets use; the UCSD number is a newer research formula.
- Check the life stage, and see the full chart below for other ages.
What formulas does the dog age calculator use?
Method 1: the size-based vet chart. This is the chart AAHA and Zoetis publish for pet owners, adapted from the Dog Owner’s Home Veterinary Handbook. It sets year 1 at 15 and year 2 at 24 for every size, then adds more years per year for bigger dogs. Between whole years we interpolate by month.
Method 2: the UC San Diego epigenetic formula.
“ln” is the natural logarithm. Wang and colleagues built the formula by comparing age-related chemical tags on DNA (methylation) in 104 Labrador Retrievers with the same tags in people. Three caveats: it came from one breed, it doesn’t account for size, and it gives nonsense below one year (ln of a number under 1 is negative). So we show it next to the chart, not instead of it.
How is the calculation done?
For the default example, a 7-year-old medium dog:
- Find the size class: a dog of 21–50 lb is medium.
- Read the size chart: first year ≈ 15, second ≈ 24, then medium dogs add about 4–5 a year. At 7 years the chart shows 47.
- For the UCSD formula, take the natural log of the age: ln(7) = 1.946.
- Multiply by 16: 16 × 1.946 = 31.1.
- Add 31: 31.1 + 31 = 62.1, so about 62.
- Life stage: a 7-year-old medium dog is a mature adult; senior care usually starts around 9 for this size.
Worked example: a 10-year-old Great Dane vs a 10-year-old Chihuahua
On the size chart, a 10-year-old small dog like a Chihuahua is 56 in human years. A 10-year-old giant dog like a Great Dane is 78. The UCSD formula gives both dogs 68, because it ignores size. The chart matches what vets see: at 10, most Chihuahuas are mature adults with years ahead, while a Great Dane is elderly.
Dog age chart: dog years to human years by size
Jump to a row with a link like #age-7. The last column is the UCSD formula, which is the same for every size.
| Dog age | Small (≤20 lb) | Medium (21–50) | Large (51–90) | Giant (>90) | UCSD formula |
|---|---|---|---|---|---|
| 1 year | 15 | 15 | 15 | 15 | 31 |
| 2 years | 24 | 24 | 24 | 24 | 42 |
| 3 years | 28 | 28 | 30 | 32 | 49 |
| 4 years | 32 | 33 | 35 | 37 | 53 |
| 5 years | 36 | 37 | 40 | 42 | 57 |
| 6 years | 40 | 42 | 45 | 49 | 60 |
| 7 years | 44 | 47 | 50 | 56 | 62 |
| 8 years | 48 | 51 | 55 | 64 | 64 |
| 9 years | 52 | 56 | 61 | 71 | 66 |
| 10 years | 56 | 60 | 66 | 78 | 68 |
| 11 years | 60 | 65 | 72 | 86 | 69 |
| 12 years | 64 | 69 | 77 | 93 | 71 |
| 13 years | 68 | 74 | 82 | 101 | 72 |
| 14 years | 72 | 78 | 88 | 108 | 73 |
| 15 years | 76 | 83 | 93 | 115 | 74 |
| 16 years | 80 | 87 | 99 | 123 | 75 |
| 17 years | 84 | 92 | 104 | – | 76 |
| 18 years | 88 | 96 | 109 | – | 77 |
| 19 years | 92 | 101 | 115 | – | 78 |
| 20 years | 96 | 105 | 120 | – | 79 |
Giant-breed values stop at 16 years because few giant dogs live longer; the calculator extends the trend if you enter an older age.
What are the life stages of a dog?
The 2019 AAHA Canine Life Stage Guidelines use five stages: puppy (until rapid growth stops, about 6–9 months), young adult (until about 3–4 years), mature adult, senior (the last 25% of expected lifespan) and end of life. Because big dogs have shorter lifespans, they become seniors sooner. The calculator uses about 10 years for small dogs, 9 for medium, 8 for large and 6 for giant breeds as the start of the senior stage. These are rough cut-offs; your vet will judge your dog as an individual.
When should you see your vet?
- Your dog is entering the senior stage. Ask about twice-yearly checkups and senior blood work.
- You notice stiffness, weight change, more drinking or peeing, confusion at night, or changes in appetite.
- You adopted a dog with an unknown age. Teeth, eyes and coat give your vet a reasonable estimate.
Frequently asked questions
How do I convert dog years to human years?
The old “multiply by 7” rule is wrong. Vet charts count the first year as about 15 human years and the second as about 24, then add 4–7 per year depending on size. Bigger dogs age faster.
What is the new dog age formula?
UC San Diego researchers (Wang et al., Cell Systems 2020) proposed human age = 16 × ln(dog age) + 31, based on DNA methylation in Labrador Retrievers. By that formula a 7-year-old dog is about 62 in human years. It isn’t meant for puppies under one year.
How old is a 7-year-old dog in human years?
Roughly 44–56 on the size-based vet chart (small to giant) and about 62 on the UCSD formula. Either way, many vets start senior screening around this age for larger dogs.
When is a dog considered a senior?
AAHA’s life stage guidelines treat roughly the last 25% of a dog’s expected lifespan as senior. That can mean about 6–7 years for giant breeds and 10 or more for small breeds.
Why do small dogs live longer than big dogs?
Large breeds seem to age faster. Several large studies show bigger dogs have shorter average lifespans, though the exact cause is still being researched.
Why do the two methods give different answers?
They measure different things. The size chart compares health and life stage, and it accounts for size. The UCSD formula compares chemical changes on DNA and was built from one breed. Treat both as rough guides, not exact ages.
Sources
- AAHA / Zoetis. “My pet’s physiological age” chart (dog chart adapted from the Dog Owner’s Home Veterinary Handbook, 4th ed., Appendix B). aaha.org
- Creevy KE, et al. 2019 AAHA Canine Life Stage Guidelines. JAAHA 2019;55(6):267–290. aaha.org
- Wang T, et al. Quantitative translation of dog-to-human aging by conserved remodeling of the DNA methylome. Cell Systems 2020;11(2):176–185. doi.org
- McMillan KM, et al. Longevity of companion dog breeds: those at risk from early death. Scientific Reports 2024;14:531. doi.org
Vet disclaimer: These are estimates for healthy pets. Your vet knows your pet. Ask them before changing diet or care, especially for puppies, kittens, seniors, pregnant pets or pets with health conditions. Read our medical disclaimer.