The ×7 rule is a 1950s myth. Dogs don't age linearly — they sprint through youth and then settle into a size-dependent pace, which is why a 1-year-old dog is a teenager and a Great Dane goes gray before a Chihuahua's midlife.
How modern conversion works
Veterinary guidance (AVMA and breed-lifespan research) maps the first dog year to about 15 human years — puberty included — and the second to ~9 more, landing a 2-year-old dog at 24. From there, size takes over: each additional year counts ~4.3 human years for small dogs but ~7 for giants. A 5-year-old small dog is ~37 human years; the same age Great Dane is ~45.
The size paradox
Across species, bigger animals usually live longer — elephants beat mice by decades. Inside the dog family the rule flips: every extra ~2 kg of adult mass trims lifespan by about a month in large-breed studies. Faster growth appears to carry faster cellular aging, which is why the calculator's size chips genuinely change the answer.
Life stages worth knowing
The stage label tracks the human-equivalent age: puppy/junior through ~13, young adult to mid-20s, adult through the 40s, and senior past ~60 — around age 6–7 for giant breeds but 10–11 for small ones. Senior status is a practical flag: vets typically recommend twice-yearly checkups from there.
About that DNA study
A 2020 UCSD study of Labrador DNA methylation proposed human age = 16 × ln(dog age) + 31 — by that curve, a 1-year-old dog is already "31." It reflects real epigenetic markers but was calibrated on a single breed, so this calculator sticks to the size-adjusted stage model vets actually use. Cat person too? The cat age calculator runs the feline version.
An estimate for healthy dogs — breed genetics and health shift individual aging.