Dog Age Calculator

The staged rule: the first year counts as about 15 human years, the second adds about 9, and each year after that adds 4 for a small dog, 5 for a medium, 6 for a large and 7.5 for a giant breed. So a 5 year old medium dog is 15 + 9 + 3 x 5, which is 39 human years - not the 35 the seven-times rule gives, and nothing like the 7 it gives for a one year old. The 2020 epigenetic formula is human age = 16 x ln(dog age) + 31. It came from comparing DNA methylation in Labradors and humans, which makes it the only version measured from biology rather than agreed by convention. Its weakness is that it was built from one breed and carries no size term.

Is one dog year really seven human years?

No, and it never was. The rule seems to have started as a marketing line to get people to bring dogs in annually. It is badly wrong for young dogs - a one year old dog is sexually mature and nearly full grown, which is an adolescent, not a first grader - and it ignores size entirely.

Why do big dogs age faster?

It is the reverse of the pattern across species, where bigger usually means longer lived, and it is still not fully explained. The leading idea is that rapid growth raises cancer risk and accelerates cellular aging. The effect is large: a Great Dane at 7 is elderly, while a Chihuahua at 7 is barely middle aged.

When is a dog a senior?

Roughly the last quarter of the expected lifespan, so about 11 for a giant breed, 8 or 9 for a large one, and 10 to 11 for a small one. Most vets switch to twice yearly checkups and senior bloodwork at that point, because a year is a bigger fraction of what is left.

What is the oldest a dog has lived?

Bluey, an Australian cattle dog, reached 29 years and 5 months. Anything past about 20 is exceptional, and small breeds hold nearly all the records, which is the size effect showing up at the far end of the curve.

Which of the two numbers should I believe?

The staged one, for a pet. It accounts for size, which is the single biggest factor, and it is what your vet is using when they talk about life stage. The epigenetic figure is the more interesting science and the less practical guide.