LifeSpan

Dog Age Calculator

The classic '15 for year one, 9 for year two, 5 per year after' rule, done precisely.

Dog's age (years)

Human-equivalent age

39 years

What you entered

Dog's age: 5 years

1
Years 1–2
15 + 9= 24 years
2
Each year after year 2
+ (3 × 5)= 39 years

Result

Human-equivalent age: 39 years

A 5-year-old dog is roughly equivalent to a 39-year-old human, using the classic 15/9/5 rule — actual aging varies a lot by breed and size, with larger breeds aging faster in later years.

Dog years converted to human-equivalent years

The first year counts for far more than later ones, so the relationship is not the familiar seven-to-one.

Dog age	Human equivalent	Life stage
1	15	Adolescent
2	24	Young adult
3	29	Adult
5	39	Adult
8	54	Mature
10	64	Senior
15	89	Geriatric

The seven-to-one rule is simply wrong, as the first two rows show: a one-year-old dog is closer to a fifteen-year-old human, and the second year adds about nine more rather than another fifteen. After that the pace settles to roughly five human years per dog year. Breed size matters enormously and this model does not capture it - small breeds commonly reach 15 or 16 years while giant breeds are often geriatric by 7, so a Great Dane at 8 is far older in practice than this table suggests.

It's an approximation

Real canine aging depends heavily on breed and size — small breeds tend to live longer and age more slowly in their later years than large breeds, which mature faster but age faster too. This calculator uses the widely cited simple version, not a size-adjusted one.

Why the first two years count for so much

Dogs reach physical and reproductive maturity within about 1-2 years, which is why the early aging rate is so much faster than a human's — a 1-year-old dog is roughly equivalent to a 15-year-old human, not a toddler.

Frequently asked questions

My dog is 7 years old — how old is that in human years?

Using the standard rule: year 1 = 15, year 2 = 9, years 3-7 = 5 each. Total: 15 + 9 + 5×5 = 49 human-equivalent years. Your dog is roughly 'middle-aged' in human terms.

Is the '7 years per dog year' rule accurate?

No — it's an oversimplification. Dogs age much faster in their first two years (reaching maturity by age 2) and then slow down. The 15/9/5 rule used here is more accurate, though even it doesn't account for breed-specific differences. A Great Dane ages much faster than a Chihuahua.

How is dog aging different from cat aging?

Dogs and cats both mature quickly in their first two years (roughly 15 + 9 human years). After that, cats age about 4 human years per calendar year while dogs age about 5. This is why indoor cats often live to 18-20 (equivalent to ~88-96 in human years). Try the cat age calculator for feline conversions.