DogYearsHow old is your dog
in human years?
Not seven times their age. Dogs race through their first two years, then age at a pace set by their size. This calculator shows you both honest methods side by side: the veterinary size chart vets actually use, and the DNA epigenetic formula from UC San Diego research.
human years. Year 1 counts as 15, year 2 brings the total to 24, then each year adds 4–7 depending on size. This is the chart most vets and kennel clubs work from.
human years, from 16 × ln(dog age) + 31. Derived from DNA methylation clocks; fitted on Labrador Retrievers, so read it as a research estimate, not a verdict.
Two methods, two answers — that gap is real. Dogs do not age on a straight line, and no single number captures it.
The full chart: dog years to human years, ages 1–20
Same numbers the calculator uses, in table form. The size columns follow the veterinary chart; the last column is the epigenetic formula, which does not vary by size.
| Dog age | Small (<20 lb) | Medium (21–50 lb) | Large (51–90 lb) | Giant (>90 lb) | DNA formula |
|---|---|---|---|---|---|
| 1 yr | 15 | 15 | 15 | 15 | 31 |
| 2 yr | 24 | 24 | 24 | 24 | 42.1 |
| 3 yr | 28 | 29 | 30 | 31 | 48.6 |
| 4 yr | 32 | 34 | 36 | 38 | 53.2 |
| 5 yr | 36 | 39 | 42 | 45 | 56.8 |
| 6 yr | 40 | 44 | 48 | 52 | 59.7 |
| 7 yr | 44 | 49 | 54 | 59 | 62.1 |
| 8 yr | 48 | 54 | 60 | 66 | 64.3 |
| 9 yr | 52 | 59 | 66 | 73 | 66.2 |
| 10 yr | 56 | 64 | 72 | 80 | 67.8 |
| 11 yr | 60 | 69 | 78 | 87 | 69.4 |
| 12 yr | 64 | 74 | 84 | 94 | 70.8 |
| 13 yr | 68 | 79 | 90 | 101 | 72 |
| 14 yr | 72 | 84 | 96 | 108 | 73.2 |
| 15 yr | 76 | 89 | 102 | 115 | 74.3 |
| 16 yr | 80 | 94 | 108 | 122 | 75.4 |
| 17 yr | 84 | 99 | 114 | 129 | 76.3 |
| 18 yr | 88 | 104 | 120 | 136 | 77.2 |
| 19 yr | 92 | 109 | 126 | 143 | 78.1 |
| 20 yr | 96 | 114 | 132 | 150 | 78.9 |
Reading example: a 5-year-old medium dog = 39 human years on the size chart. A 3-year-old on the DNA formula = about 48.6.
Why “multiply by 7” is wrong
Dogs front-load their ageing. A puppy reaches sexual maturity within its first year — no seven-year-old human does that. Vets have long used a curve instead: the first year of a medium dog's life is roughly equivalent to 15 human years, the second year adds about 9 more (24 total), and only after that does each year settle into a steadier 4–7 human years, with the exact pace set by body size.
Size matters more as dogs get older. A 10-year-old Chihuahua and a 10-year-old Great Dane have lived the same decade but not the same ageing: the chart puts them at about 56 and 72 human years respectively, which matches their very different typical lifespans.
The DNA formula tells a third story. In 2020, researchers at UC San Diego compared methylation patterns — chemical marks on DNA that change predictably with age — across dogs and humans, producing the formula 16 × ln(dog age) + 31. It captures how ageing is fastest at the very start of life. It was fitted on 104 Labrador Retrievers, a single large breed, so it cannot see size differences at all. We show it because it is real science and often quoted — labelled, with its limits attached.
None of these numbers is a health assessment. They are comparison tools — useful for understanding what stage of life your dog is in, and for deciding when to start conversations with your vet about senior care.
Keep exploring
Questions, answered straight
Is one dog year really equal to seven human years?
No. The ×7 rule is a rough old shortcut that does not match how dogs actually age. Dogs mature very fast in their first two years — a one-year-old dog is closer to a 15-year-old human — and then ageing slows down and depends on body size. Both methods on this page reflect that curve instead of a straight line.
Which method should I use, the size chart or the DNA formula?
Use the size chart for everyday comparisons, because it accounts for the fact that large dogs age faster than small ones. The epigenetic formula comes from DNA methylation research and is a fascinating cross-check, but it was fitted on Labrador Retrievers only, so treat it as an estimate with a lab-shaped bias. Where the two disagree, the honest answer is somewhere in that range.
How old is a 5-year-old dog in human years?
It depends on size. By the veterinary size chart, a 5-year-old dog is about 36 in human years if small, 39 if medium, 42 if large and 45 if giant. The epigenetic formula gives about 56.8 regardless of size, which is one reason scientists say the two methods measure slightly different things.
Why do big dogs age faster than small dogs?
Larger breeds grow faster and tend to develop age-related conditions earlier, and their typical lifespans are shorter — often 7–10 years for giant breeds versus 14–16 for the smallest. The size chart builds that in by adding more human years per dog year as size increases.
How old is my dog in human years if they are 10?
By the size chart: about 56 for a small dog, 60 for a medium dog, 66 for a large dog and 72 for a giant breed. By the epigenetic formula, about 67.8. Most 10-year-old dogs are considered senior or close to it, so it is a good age to talk to your vet about senior screening.
Can this calculator tell me when my dog becomes a senior?
It gives the commonly used size-based guide — roughly 11 for small dogs, 10 for medium, 8 for large and 6 for giant breeds — but 'senior' is a care decision, not just a number. Your vet will weigh breed, weight, mobility and bloodwork, and may start senior checks earlier or later than the chart suggests.