How we calculate your dog's age

Why 1 dog year isn't 7 human years

The times-seven rule assumes dogs age at the same pace throughout life. They don't. A one-year-old dog is usually sexually mature and nearly full-grown, while a seven-year-old child is far from adult. And a two-year-old dog is much more like a person in their mid-twenties than a fourteen-year-old.

The rule also misses the difference between breeds. A small dog at ten may still be lively with many years ahead, while a giant dog of the same age is often well into its senior years.

Why dogs age faster early in life

In its first year a puppy goes from completely helpless to an active, sexually mature dog. In the second year it finishes growing and matures mentally. That much development in so little time corresponds to a large part of a human's childhood and adolescence.

After that, development levels off and each new year brings less change. Research on DNA methylation (Wang et al., 2020) shows the same pattern: fast aging early, slower later.

Why size and breed affect aging

Among dogs, small breeds generally live longer than large ones — the opposite of the pattern between species, where large animals often live longest. Studies of lifespan and causes of death (Greer et al., 2007; Fleming et al., 2011) show a clear link between body size and lifespan. Why this happens is still not fully explained.

Breed matters beyond size too. Some breeds are predisposed to certain conditions, and dogs of the same breed can age differently because of genetics, weight, activity and care. That's why every number in the calculator is an estimate.

There are several ways to compare dog years and human years

The 1:7 rule is a very rough rule of thumb. It ignores the fact that dogs mature quickly early in life and that breeds age differently.

Published veterinary guidance: The AVMA, as presented by the American Kennel Club, assumes faster aging in the first years: about 15 human years for the first year, around 9 for the second, then roughly 5 per year for a medium-sized dog.

Scientific research: Wang et al. (2020) studied aging in a different way — through age-related changes in DNA methylation in 104 Labrador Retrievers — and found a logarithmic relationship with human aging: human age = 16 × ln(dog age) + 31. The study is based on a single breed, so the formula can't automatically be used as an exact human age for every breed, and more research is needed on other breeds. The calculator does not use it.

Size-adjusted model (used by the calculator): 15 human years at age 1 and 24 at age 2 for every size, then 4 (small), 5 (medium), 6 (large) or 7.5 (giant) human years per year.

None of these models gives an exact, individual 'human age'. Dogs of different sizes and breeds do not age at exactly the same rate. Larger dogs generally have shorter lifespans and are often considered senior earlier. For this reason, any human-age conversion is an estimate rather than an exact biological measurement.

The model in three steps

1. 1

   First year ≈ 15 human years

   The first dog year counts as about 15 human years, regardless of breed. For puppies under one year it is calculated proportionally by month.

2. 2

   Second year adds ≈ 9 years

   The second year adds around 9 human years, so a two-year-old dog corresponds to about 24 human years. Up to this point the curve is the same for all sizes.

3. 3

   From year three: 4–7.5 human years per year

   Each dog year after age two adds 4 (small), 5 (medium), 6 (large) or 7.5 (giant) human years, depending on the breed's size.

A worked example

Let's calculate the age of a 5-year-old Labrador Retriever:

First year

15 human years

Second year

+ 9 human years (= 24)

Years 3 to 5 (3 × 6)

+ 18 human years

Total

42 human years

So a 5-year-old Labrador corresponds to roughly a 42-year-old person. As a large breed, it gains 6 human years per year from year three. A small dog of the same age corresponds to 36, and a giant dog to 46.5.

Dog years to human years

Figures are estimated human years by size. The calculator, the homepage and the breed pages all use exactly the same calculation.

What the model is based on

Model and source: 15 human years for the first year, around 9 for the second (24 in total) for every size, then 4 (small), 5 (medium), 6 (large) or 7.5 (giant) per year. The first two years are based on AVMA veterinary guidance as presented by the American Kennel Club in 'How to Calculate Dog Years to Human Years'. From year 3 onward, the size-adjusted rates are our own estimation model, not official AVMA or AKC figures. The model is a rough estimate.

Why size matters: Larger dogs live shorter lives on average and age faster after the first years. That is why more human years are added per year the larger the breed.

Size and breed: Larger dogs live shorter lives on average (Greer et al., 2007; Fleming et al., 2011) and are often considered senior earlier. Breed, size, genetics, health and the individual dog all affect how a dog ages. The calculator uses the breed's typical size to estimate life stage and senior age: small under 10 kg, medium 10–25 kg, large 25–45 kg and giant over 45 kg.

Life stages: The division into puppy, adult, mature and senior builds on the AAHA Canine Life Stage Guidelines (2019), which link senior age to the last quarter of expected lifespan.

Limitations of the model

• The model uses four size groups. It doesn't capture differences between breeds of the same size or between individual dogs.
• The life stage uses four size classes. Dogs that fall between two classes, and mixed breeds, don't always fit perfectly.
• It doesn't account for individual health, weight, diet, activity level, neutering or inherited conditions.
• The fixed yearly increase is a simplification. In reality, aging levels off more gradually.
• The age at which a breed is considered senior is approximate and varies between sources and between individual dogs.