Dog Age Calculator
How old is your dog, really? The “multiply by 7” rule everyone learned is wrong at both ends of a dog's life. Compare it against the 2020 epigenetic-clock formula and the veterinary size table to get a far better answer.
Epigenetic clock
56.8
16 × ln(age) + 31 · 2020 UCSD study
Vet rule of thumb (medium)
36
15 + 9, then +4/yr
The old ×7 rule
35
a myth — aging isn't linear
Why they disagree: dogs age explosively early and slowly later. The epigenetic clock says a 1-year-old dog is biologically ~31 human years, then each doubling of dog age adds only ~11 more. The ×7 rule misses both ends.
The epigenetic formula comes from DNA-methylation data in Labrador retrievers (Cell Systems, 2020) — other breeds, especially giant ones, likely sit somewhat off that curve. The size-based schedule shown is the common veterinary rule of thumb, not a measurement.
Why a Logarithm Beats Multiplying by 7
Dogs sprint through youth and then coast: a dog can reproduce before its first birthday, which no “7-year-old human” can. The 2020 UC San Diego study matched DNA-methylation patterns in Labrador retrievers against humans and found aging follows a logarithmic curve: human age = 16 × ln(dog years) + 31. That makes a 1-year-old dog biologically ~31 human years and a 5-year-old 16 × ln(5) + 31 ≈ 56.8 — about 57, not the 35 the ×7 myth claims. Because the data came from one breed, vets still lean on the size-based schedule for everyday use, since big dogs genuinely age faster than small ones.
Veterinary rule of thumb (schedule used above)
Year 1 ≈ 15 human years Year 2 +9 (24 total) Each year after: small/medium dogs +4 per year (5 yr ≈ 36) large 51–90 lb +5 per year (5 yr ≈ 39) giant >90 lb +7 per year (5 yr ≈ 45) Epigenetic clock: human age = 16 × ln(dog years) + 31
Frequently Asked Questions
How old is a 7-year-old dog in human years?
By the epigenetic-clock formula, 16 × ln(7) + 31 ≈ 62 human years — far older than the 49 the old ×7 rule suggests. The veterinary size table lands lower: about 44 for a small or medium dog, 49 for a large one. The honest answer is a range of roughly 44–62 depending on method and size, with the science pointing toward the higher end.
Is the 7-year rule for dog years accurate?
No — it's a marketing-era simplification that fails at both ends of a dog's life. Dogs can reproduce before their first birthday, so a 1-year-old dog is biologically closer to a human in their late twenties (the epigenetic formula says ~31) than to a 7-year-old child. Aging then slows dramatically: from age 2 to 5, a dog gains only about 15 'human years', not 21.
Do big dogs really age faster than small dogs?
Yes — it's one of biology's odd inversions, since across species larger animals usually live longer. Within dogs, giant breeds like Great Danes average 7–10 years while small breeds often reach 14–16, so vets advance giant breeds roughly +7 human years per dog year after age two versus +4 for small dogs. That's why a 5-year-old Great Dane (~45 human years) counts as approaching senior while a 5-year-old terrier (~36) is solidly middle-aged.
How accurate is the epigenetic dog age formula?
The 2020 UC San Diego study behind it compared DNA-methylation patterns — chemical aging marks on the genome — between 104 Labrador retrievers and a human cohort, producing human age = 16 × ln(dog years) + 31. It's the best biologically grounded conversion available, but it was derived from a single breed, so small and giant breeds likely sit somewhat off the curve. Treat it as a well-founded estimate, not a measurement.