How old is my dog in human years?

About 15 at one year and 24 at two, a little less for giant breeds. After that it depends on size: small dogs add about 4 years a year and giant breeds 7 or 8, so at 10 a small dog is about 56 and a giant breed about 79.

How old is my cat in human years?

About 15 at one year and 24 at two, then about 4 human years for each year after that. A 10-year-old cat is about 56.

Is one dog year really seven human years?

No. That old rule is too simple: dogs grow up fast in their first two years, and bigger breeds age faster after that.

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How old is your pet in human years?

For dogs of every size and for cats, using the guidelines vets use. Free, nothing to sign up for.

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Pet age chart

A pet's age and its equivalent in human years, for cats and for dogs by size
Age	Cat	Small dog	Medium dog	Large dog	Giant dog
1 year	15	15	15	15	12
2 years	24	24	24	24	22
3 years	28	28	28	28	31
4 years	32	32	32	32	38
5 years	36	36	36	36	45
6 years	40	40	42	45	49
7 years	44	44	47	50	56
8 years	48	48	51	55	64
9 years	52	52	56	61	71
10 years	56	56	60	66	79
11 years	60	60	64	71	87
12 years	64	64	68	76	95
13 years	68	68	72	81	103
14 years	72	72	76	86	111
15 years	76	76	80	91	119
16 years	80	80	84	96	127

Dog sizes by adult weight: small up to 20 lb (9 kg); medium 21 to 50 lb (10 to 23 kg); large 51 to 90 lb (23 to 41 kg); giant over 90 lb (41 kg).

Questions

How old is my dog in human years?: About 15 at one year and 24 at two, a little less for giant breeds. After that it depends on size: small dogs add about 4 years a year and giant breeds 7 or 8, so at 10 a small dog is about 56 and a giant breed about 79.
How old is my cat in human years?: About 15 at one year and 24 at two, then about 4 human years for each year after that. A 10-year-old cat is about 56.
Is one dog year really seven human years?: No. That old rule is too simple: dogs grow up fast in their first two years, and bigger breeds age faster after that.

Sources: for dogs, the American Veterinary Medical Association's rule of thumb for the first two years (about 15 human years, then 9 more) and, after that, the dog size chart many vets use, where bigger breeds age faster; for cats, the AAHA and AAFP feline life stage guidelines. These are rules of thumb: your vet knows your pet best.