Dog Age Calculator
Enter your dog's age and adult size. You get the veterinary size-adjusted conversion, the 2020 UCSD epigenetic formula, and the old 'times 7' number so you can see how far off it is.
Size-adjusted chart (vet convention)
39 human years
Medium dog
UCSD epigenetic formula (2020)
57 human years
16 × ln(5) + 31
The old 'times 7' rule
35 human years
shown for comparison only
Dog years to human years, by size
The veterinary convention: the first year counts as 15 human years, the second as 9 more (24 by age two), and every year after that as 4, 5, 6 or 7 depending on adult size. The last column is the UCSD epigenetic formula for comparison -- it agrees with the chart in the middle years and diverges at both ends.
| Dog age | Small | Medium | Large | Giant | UCSD formula |
|---|---|---|---|---|---|
| 1 | 15 | 15 | 15 | 15 | 31 |
| 2 | 24 | 24 | 24 | 24 | 42 |
| 3 | 28 | 29 | 30 | 31 | 49 |
| 4 | 32 | 34 | 36 | 38 | 53 |
| 5 | 36 | 39 | 42 | 45 | 57 |
| 6 | 40 | 44 | 48 | 52 | 60 |
| 7 | 44 | 49 | 54 | 59 | 62 |
| 8 | 48 | 54 | 60 | 66 | 64 |
| 9 | 52 | 59 | 66 | 73 | 66 |
| 10 | 56 | 64 | 72 | 80 | 68 |
| 11 | 60 | 69 | 78 | 87 | 69 |
| 12 | 64 | 74 | 84 | 94 | 71 |
| 13 | 68 | 79 | 90 | 101 | 72 |
| 14 | 72 | 84 | 96 | 108 | 73 |
| 15 | 76 | 89 | 102 | 115 | 74 |
| 16 | 80 | 94 | 108 | 122 | 75 |
Life stages by size
What the human-years number is actually for: knowing when your dog crosses into the stage where care changes. Puppyhood ends at roughly 12 months for small breeds and up to 24 for giants; adulthood runs until the senior threshold below; beyond that, twice-yearly vet visits and baseline bloodwork are the usual recommendation.
| Size | Typical adult weight | Puppy until | Senior from | Typical lifespan |
|---|---|---|---|---|
| Small | under 20 lb | 9-12 months | 10-11 years | 12-16 years |
| Medium | 20-50 lb | 12 months | 8-10 years | 11-14 years |
| Large | 50-90 lb | 12-18 months | 7-8 years | 10-12 years |
| Giant | over 90 lb | 18-24 months | 5-6 years | 7-10 years |
Worked example
A 6-year-old Labrador (large): chart method 15 + 9 + 4 × 6 = 48 human years; UCSD method 16 × ln(6) + 31 = 16 × 1.79 + 31 = 60. The old rule would say 42. Both modern methods put this dog in late middle age, a year or two from the senior threshold for large breeds -- which is the useful conclusion.
Frequently Asked Questions
Why is 'multiply by 7' wrong?
Because dogs don't age at a constant rate. A one-year-old dog is sexually mature and roughly equivalent to a 15-year-old human, not a 7-year-old; after the first two years the rate slows to about 4-7 human years per dog year depending on size. The ×7 rule undercounts young dogs and overcounts old small dogs.
Which method should I trust?
Use the size-adjusted chart for everyday purposes -- it is the convention vets use for life-stage decisions like when to start senior screening. The UCSD formula is a genuine research result (from DNA methylation in Labradors) but it was fit to one breed and behaves oddly at the extremes; it is best read as a second opinion for medium and large dogs.
Why do big dogs age faster?
Larger breeds have shorter lifespans -- a Great Dane's median is around 7-8 years, a Chihuahua's 14-16 -- so each calendar year is a bigger share of their life. The size-adjusted chart reflects that by adding 4 human years per dog year for small breeds and 7 for giants after age two.
When is my dog a senior?
Roughly when it reaches the last quarter of its expected lifespan: small breeds around 10-11, medium around 8-10, large around 7-8, giant breeds as early as 5-6. That is the point most vets recommend twice-yearly checkups and baseline bloodwork.
What is the 16 ln(age) + 31 formula?
It comes from a 2020 study at UC San Diego (Wang et al., Cell Systems) that compared DNA methylation patterns -- an 'epigenetic clock' -- in 104 Labrador retrievers to those in humans. The natural log means dog age is compressed early and stretched later: 1 year maps to 31, 2 to 42, 5 to 57, 10 to 68.
These calculators use published veterinary formulas and are for general guidance. They are not a diagnosis and do not replace your veterinarian, who knows your animal's breed, history, and body condition.