How this dog age calculator works

Dogs don’t age at a steady pace. They race through childhood, then slow down. A one-year-old dog can usually have puppies of its own and has a full set of adult teeth, which puts it closer to a 15-year-old person than a 7-year-old. By the second birthday most dogs are roughly the human equivalent of their mid-twenties.

After that, size takes over. Small dogs age slowly and often live into their mid-teens. Giant breeds age fast and are often seniors by six or seven. That’s why the calculator asks for your dog’s adult size, not just its age.

The main number on the tag comes from the size-based chart published by the American Animal Hospital Association (AAHA). For ages between whole years, we fill the gap in a straight line. For puppies under one, we spread the first year’s 15 human years evenly, so treat puppy results as a rough guide.

Dog years to human years chart

Here’s the full chart if you’d rather look it up yourself. Weights are the dog’s expected adult weight.

Dog age	Small (≤20 lb)	Medium (21–50 lb)	Large (51–90 lb)	Giant (90+ lb)
1	15	15	15	15
2	24	24	24	24
3	28	28	30	32
4	32	33	35	37
5	36	37	40	42
6	40	42	45	49
7	44	47	50	56
8	48	51	55	64
9	52	56	61	71
10	56	60	66	78
11	60	65	72	86
12	64	69	77	93
13	68	74	82	101
14	72	78	88	108
15	76	83	93	115
16	80	87	99	123

Look at the gap by age 10. A 10-year-old Chihuahua is about 56 in human terms. A 10-year-old Great Dane is about 78. Same birthday, very different body.

What about the DNA-clock formula?

In 2020, researchers at the University of California San Diego published a study that compared chemical changes on DNA in Labrador Retrievers and people. They came up with this formula:

human age = 16 × ln(dog age) + 31

“ln” is the natural logarithm, which is why the curve rises so steeply early on. Under this formula a one-year-old dog is about 31 and a seven-year-old is about 62. We show it under the tag as a second opinion, but keep in mind it was built from one breed, so it doesn’t account for size.

So which number is right? Neither is exact. The chart is better for comparing dogs of different sizes. The DNA formula is a good reminder that young dogs mature much faster than most people think.

Dog life stages and why they matter

Knowing your dog’s age in human years is fun, but life stage is the part that changes how you care for them. AAHA groups dogs roughly like this:

Puppy: birth to the end of fast growth, which can run past a year in big breeds.
Young adult: from the end of growth to about three or four.
Mature adult: the long middle stretch, until the last quarter of expected lifespan.
Senior: the last 25% of expected lifespan. That’s why a Great Dane can be a senior at seven while a Jack Russell isn’t one until ten or later.

Once your dog reaches the senior stage, most vets suggest checkups every six months instead of once a year. Problems like kidney disease, arthritis and dental pain tend to show up slowly, and older dogs are good at hiding them.

A quick example: Max is an 8-year-old Labrador, about 75 lb, so he’s in the large group. The chart puts him at about 55 human years, and he’s right at the start of his senior stage. That’s a good time to ask the vet about bloodwork and joint care, even if he still acts like a puppy at the park.

Signs your dog is getting older

Numbers aside, your dog’s body tells you a lot. Watch for:

Grey hair around the muzzle and eyes
Stiffness after naps, or trouble with stairs and car jumps
Cloudy-looking eyes (often harmless, but worth mentioning to your vet)
Sleeping more, or a change in appetite or thirst
Bad breath or chewing on one side of the mouth

Increased thirst in particular is worth a vet visit at any age. It can point to kidney problems, diabetes or hormone conditions that are easier to manage when caught early.

Common questions

Is one dog year really seven human years?

No. The 7:1 rule is an old shortcut that probably came from comparing average lifespans. It badly underestimates young dogs and gets large breeds wrong at every age.

How old is a 1-year-old dog in human years?

About 15, whatever the size. Most dogs are physically mature, or close to it, by their first birthday.

What if my dog is a mixed breed?

Pick the size that matches your dog’s adult weight. Size is a better guide to aging than breed for most mixed-breed dogs.

My puppy isn’t fully grown yet. Which size do I choose?

Choose the size you expect your dog to reach as an adult. Our puppy weight calculator can give you an estimate.

How long do dogs live?

Many small dogs live 13 to 16 years, medium dogs 11 to 14, large dogs 10 to 12 and giant breeds 8 to 10. Genetics, weight, dental care and luck all play a part.

Can I use this for cats?

No. Cats age on a different curve. Try the cat age calculator instead.

Sources

Last reviewed November 4, 2026.

Dog age	Small (≤20 lb)	Medium (21–50 lb)	Large (51–90 lb)	Giant (90+ lb)
1	15	15	15	15
2	24	24	24	24
3	28	28	30	32
4	32	33	35	37
5	36	37	40	42
6	40	42	45	49
7	44	47	50	56
8	48	51	55	64
9	52	56	61	71
10	56	60	66	78
11	60	65	72	86
12	64	69	77	93
13	68	74	82	101
14	72	78	88	108
15	76	83	93	115
16	80	87	99	123

Dog age	Small (≤20 lb)	Medium (21–50 lb)	Large (51–90 lb)	Giant (90+ lb)
1	15	15	15	15
2	24	24	24	24
3	28	28	30	32
4	32	33	35	37
5	36	37	40	42
6	40	42	45	49
7	44	47	50	56
8	48	51	55	64
9	52	56	61	71
10	56	60	66	78
11	60	65	72	86
12	64	69	77	93
13	68	74	82	101
14	72	78	88	108
15	76	83	93	115
16	80	87	99	123

Dog age	Small (≤20 lb)	Medium (21–50 lb)	Large (51–90 lb)	Giant (90+ lb)
1	15	15	15	15
2	24	24	24	24
3	28	28	30	32
4	32	33	35	37
5	36	37	40	42
6	40	42	45	49
7	44	47	50	56
8	48	51	55	64
9	52	56	61	71
10	56	60	66	78
11	60	65	72	86
12	64	69	77	93
13	68	74	82	101
14	72	78	88	108
15	76	83	93	115
16	80	87	99	123