How Old Is My Dog in Human Years? Full Chart by Size
To find your dog’s age in human years, look up its age and adult weight on the American Animal Hospital Association (AAHA) age chart. Every dog is about 15 in human years at age 1 and about 24 at age 2. After that the answer depends on size, because bigger dogs age faster. The quickest way is the dog age calculator, which reads the same chart for you and handles extra months too.
Below is the full chart, how to pick the right size group, what to do with a puppy under one year, and how to tell when your dog has become a senior.
The dog age chart by size
The AAHA chart, published with the 2019 Canine Life Stage Guidelines, splits dogs into four groups by adult weight. Find your dog’s age on the left, then read across to its size group.
| Dog’s age | Up to 20 lb | 21–50 lb | 51–90 lb | Over 90 lb |
|---|---|---|---|---|
| 1 year | 15 | 15 | 15 | 15 |
| 2 years | 24 | 24 | 24 | 24 |
| 3 years | 28 | 28 | 30 | 32 |
| 4 years | 32 | 33 | 35 | 37 |
| 5 years | 36 | 37 | 40 | 42 |
| 6 years | 40 | 42 | 45 | 49 |
| 7 years | 44 | 47 | 50 | 56 |
| 8 years | 48 | 51 | 55 | 64 |
| 9 years | 52 | 56 | 61 | 71 |
| 10 years | 56 | 60 | 66 | 78 |
| 11 years | 60 | 65 | 72 | 86 |
| 12 years | 64 | 69 | 77 | 93 |
| 13 years | 68 | 74 | 82 | 101 |
| 14 years | 72 | 78 | 88 | 108 |
| 15 years | 76 | 83 | 93 | 115 |
| 16 years | 80 | 87 | 99 | 123 |
The chart goes on to 20 years for the three smaller groups. For dogs over 90 lb it stops at 16, so the calculator extends the last step of the chart for any older giant dog and tells you it has done so.
How to read the chart for your dog
- Work out your dog’s age in years and months. If you don’t know the birthday, use the age on adoption papers or a vet record and count forward from there.
- Pick the size group from adult weight. Use what your dog weighs (or will weigh) as a grown dog, not what it weighed at its last visit as a puppy.
- Find the row for the whole years. That is the human age at your dog’s last birthday.
- Add the months if you want more detail. The calculator moves in a straight line between two years. A dog that is halfway between birthdays sits halfway between the two chart values.
Choosing between two size groups
The size lines on the chart are 20 lb, 50 lb and 90 lb (about 9, 23 and 41 kg). If your dog sits close to a line, try both groups in the calculator. The difference at young ages is small; it grows as dogs get older, especially between the 51–90 lb and over 90 lb groups.
Mixed-breed dogs use the chart the same way as purebreds. The chart is based on weight, so you don’t need to know the breed.
What about puppies under one year?
The AAHA chart starts at 1 year. For younger puppies the calculator draws a straight line from birth to 15 at the first birthday, so it uses this formula:
Human years = dog’s age in years × 15
Treat that as a rough guide only. Puppies grow up in bursts, not in a straight line, and the real point of the first year is simple: by the first birthday a dog is roughly like a teenager in human terms.
Why size changes the answer
Small and medium dogs add about 4 to 5 human years for each year after age 2 on the chart. Large dogs add a little more, and dogs over 90 lb add the most. The pattern matches what lifespan studies show: large and giant breeds tend to have shorter lives than small breeds, so each year of their life covers more ground.
That is why the old “multiply by 7” rule doesn’t work. It makes young dogs too young and old small dogs too old, and it gives a Chihuahua and a Great Dane the same answer. If you want the full story behind the myth, read Is 1 Dog Year Really 7 Human Years?.
The DNA-clock formula, as a second opinion
The calculator also shows a second result from a 2020 study by Wang and colleagues in the journal Cell Systems. The researchers compared chemical changes on DNA (methylation) in dogs and people as they age, and fitted this formula:
Human age = 16 × ln(dog’s age) + 31
Here “ln” is the natural logarithm, the “ln” key on any scientific calculator. The formula only works from age 1, and it was built from Labrador Retrievers, so it is an interesting comparison rather than a rule for every dog. It agrees with the chart on the main point: dogs age very fast early on and more slowly later.
Life stages: when is a dog a senior?
Human years are fun to know, but the life stage is what matters for care. The calculator uses the AAHA life stages:
| Life stage | When it starts |
|---|---|
| Puppy | Birth to 9 months |
| Young adult | 9 months to 3½ years |
| Mature adult | 3½ years until the senior stage |
| Senior | The last 25% of the typical lifespan for the dog’s size |
For the senior line, the calculator uses the median lifespan for each size group from a 2024 study of UK dogs (McMillan and colleagues, Scientific Reports). Senior starts at 75% of that figure:
Senior from = median lifespan for the size × 0.75
With the calculator’s figures, that works out to about 9½ years for dogs up to 20 lb, a little over 9 for 21–50 lb dogs, about 9 for 51–90 lb dogs and about 7½ for dogs over 90 lb. The giant figure is the calculator’s own estimate, built from the same study’s results for Great Danes, Newfoundlands, St Bernards and Mastiffs. For your own dog’s breed, the dog life expectancy calculator gives the median for 49 breeds and the matching senior age.
What changes at the senior stage
Vets usually suggest more frequent check-ups for senior dogs, because changes in weight, teeth, joints, kidneys and eyesight are easier to manage when they are caught early. Ask your vet how often your dog should come in once it reaches this stage.
Tips for getting a useful answer
- Use adult weight, not breed averages. A large-framed dog of a small breed can belong in the next group up.
- Round down if you’re unsure of the birthday. It is better to plan senior care slightly early than late.
- Compare with your cat. Cats age on a different curve, covered in How Old Is My Cat in Human Years? and the cat age calculator.
- Don’t read too much into a single number. Human years are a comparison, not a medical measure. Your dog’s health, weight and activity tell you more.
Frequently asked questions
How old is a 1-year-old dog in human years?
About 15, whatever its size. On the AAHA chart every dog is 15 at its first birthday and 24 at its second. The size groups only start to split from age 3.
Do small dogs or big dogs age faster?
Big dogs. After age 2, dogs over 90 lb add the most human years per year on the AAHA chart, and dogs up to 20 lb add the fewest. Larger breeds also tend to have shorter lifespans on average.
My dog’s weight is right on the line between two groups. Which should I use?
Try both in the dog age calculator and you will see the range. If your dog is near the line only because it is a little over or under its ideal weight, use the group for its ideal adult weight.
Is the DNA formula more accurate than the chart?
Not for every dog. It was built from one breed, Labrador Retrievers, and it gives older-sounding ages for young dogs than the chart does. Vets still use size-based charts like AAHA’s. The calculator shows both so you can compare.
At what age should my dog start senior check-ups?
The AAHA guidelines count a dog as a senior in the last 25% of its expected lifespan, which comes sooner for bigger dogs. Check with your vet about when to start senior check-ups and how often, since your dog’s own health matters more than the chart.