Dog years to human years: chart by size

One dog year is not seven human years. A dog's first year is worth about 15 human years, the second about 9, and every year after that adds 4 to 6 depending on the dog's size. So a 10-year-old small dog is about 56 in human years, and a 10-year-old giant breed is about 72.

The chart below gives the number for every age from 1 to 20. For an answer that uses your dog's breed, including when that breed becomes a senior, use the pet age calculator.

Dog years to human years chart

Find your dog's age in the left column, then read across to its size. All numbers are human years.

The chart runs to 20 for completeness. Few large dogs and very few giant dogs reach the ages at the bottom of their columns, which is why those numbers pass 100.

Which size is my dog?

These are the weight bands this site uses, based on healthy adult weight:

• Small: under 20 lb
• Medium: 20 to 50 lb
• Large: 50 to 90 lb
• Giant: over 90 lb

For a mixed-breed dog, go by adult weight. If your dog sits on a line between two sizes, the two columns are close enough that either gives a fair answer.

How to calculate dog years

You can work it out without the chart:

1. Count 15 human years for the first year.
2. Add 9 for the second year, which makes 24 at age two.
3. For each year after that, add 4 for a small dog, 4.5 for a medium dog, 5 for a large dog or 6 for a giant dog.
4. Round to the nearest whole number, with halves rounded up.

A 9-year-old Labrador is a large dog, so the sum is 15 + 9 + (7 x 5) = 59. This is the same math the calculator on this site uses.

How long is a dog year?

It changes as the dog gets older. In the first calendar year a dog ages about 15 human years. In the second it ages about 9. After that, one calendar year is worth 4 to 6 human years.

Put the other way round, an adult small dog ages one human year about every three months, and an adult giant dog about every two.

What is 1 year in dog years?

A 1-year-old dog is about 15 in human years, whatever its size. That fits what you see: a one-year-old dog is close to fully grown and behaves like a teenager, not a first grader.

How old is my dog in human years? Common ages

• How old is 3 in dog years? About 28 for a small dog, 29 for a medium or large dog and 30 for a giant dog.
• 5 in dog years: 36 small, 38 medium, 39 large, 42 giant.
• How old is 6 in dog years? 40 small, 42 medium, 44 large, 48 giant.
• 13 in dog years: 68 small, 74 medium, 79 large, 90 giant.
• How old is 15 in dog years? 76 small, 83 medium, 89 large, 102 giant.
• 16 in dog years: 80 small, 87 medium, 94 large, 108 giant.
• 18 in dog years to human years: 88 small, 96 medium, 104 large, 120 giant. An 18-year-old dog of any size is very old.

Human years to dog years

To go the other way, find the human age in the chart and read back to the left column. Some examples:

• 40 in human years is about a 6-year-old small dog or a 5-year-old large or giant dog. A medium dog falls between 5 and 6.
• 50 is about an 8-year-old medium dog, a 7-year-old large dog or a 6-year-old giant dog. A small dog falls between 8 and 9.
• 60 is about an 11-year-old small dog, a 10-year-old medium dog, a 9-year-old large dog or an 8-year-old giant dog.
• 80 is about a 16-year-old small dog, a 14-year-old medium dog, a 13-year-old large dog or an 11-year-old giant dog.

Why the 7-year rule is wrong

The rule probably started as simple division: people live to about 70, dogs to about 10. It is easy to remember and wrong at both ends.

Dogs grow up fast and then age more slowly. By the 7-year rule a 1-year-old dog would be a 7-year-old child, yet many dogs are physically able to have puppies by then. And one multiplier cannot fit every dog, because a Chihuahua and a Great Dane of the same age are at very different points in their lives.

Why big dogs age faster

Among dogs, larger breeds tend to have shorter lives than smaller ones. In the breed guides on this site, typical lifespans for giant breeds run from 6 to 12 years, while several small breeds commonly reach 14 to 16.

The reasons are not fully understood. The leading explanations involve how quickly large dogs grow and how early age-related disease tends to appear in them. Whatever the cause, the practical effect is that a large dog reaches each life stage sooner.

That is why size decides when a dog is considered a senior: around 10 for most small breeds, 8 for medium, 7 for large and 5 or 6 for giant. In human years that is somewhere in the 40s or 50s.

What the chart can and cannot tell you

The chart is an estimate of life stage, not a health assessment. Two dogs of the same age and size can be in very different shape, and breed, weight and health history all matter more than a number in a table.

Use it to decide when to change the routine. Once your dog reaches senior age for its size, it is worth reading the senior dog guide, asking your vet about twice-yearly checkups, and looking at what to look for in a senior dog food. Sudden changes at any age, such as not eating, new stiffness or confusion, are a reason to call your vet and not something to put down to age.

If you do not know your dog's age, which is common with rescues, your vet can estimate it from teeth, eyes and body condition. If you are thinking of taking on an older rescue, see adopting a senior dog. Have a cat as well? The math is different, and the cat years to human years chart covers it.

Get a breed-specific answer

The chart works from size alone. The dog years calculator takes your dog's breed and age and gives the human-years figure, the life stage for that breed and how often a dog at that stage usually sees the vet.

This chart is general educational information, not veterinary advice. Human-year equivalents are estimates based on averages for a dog's size and say nothing about the health of an individual dog. Your veterinarian is the right person to assess your dog's age, condition and care.