How old is my dog in human years?

This dog years calculator is also a cat age calculator. It shows your pet's age in human years, its life stage and a curve with your pet marked on it. Everything runs in your browser and your last settings are kept. The result is an estimate: every animal ages at its own pace.

How to use it

Under "Pet", choose "Dog" or "Cat".
For a dog, pick the "Dog size" from its adult weight: "Small" (under 10 kg, about 22 lb), "Medium" (22–55 lb), "Large" (55–100 lb) or "Giant" (over 100 lb).
Fill in "Years" and "Months", or switch to "Its date of birth": the exact age is counted up to today.
Read the "Age in human years", the life stage and the worked calculation. The box "Other method: logarithmic formula (dogs)" adds a second estimate.

Why "one year equals seven" is wrong

At one year, a dog or cat is almost full grown and able to breed: far closer to a 15-year-old than a 7-year-old. The first two years count for a lot, then ageing slows down. Later on, the rule of seven makes every 10-year-old dog 70, when a small dog of that age is more like 56 and a giant dog 80.

The calculator follows a convention widely used by vets: 1 year = 15 human years, 2 years = 24, then 4 more per year for a cat, and 4, 5, 6 or 7 for a dog depending on size. Months count pro rata, in a straight line from 0 to 15 in the first year and from 15 to 24 in the second. A 6-month-old kitten is 15 × 6/12 = 7.5 in human years; a large dog aged 5 years and 6 months is 24 + 6 × 3.5 = 45.

Dog and cat age chart

Real age	Cat	Small dog	Medium dog	Large dog	Giant dog
1 year	15	15	15	15	15
2 years	24	24	24	24	24
3 years	28	28	29	30	31
4 years	32	32	34	36	38
5 years	36	36	39	42	45
6 years	40	40	44	48	52
7 years	44	44	49	54	59
8 years	48	48	54	60	66
9 years	52	52	59	66	73
10 years	56	56	64	72	80
11 years	60	60	69	78	87
12 years	64	64	74	84	94
13 years	68	68	79	90	101
14 years	72	72	84	96	108
15 years	76	76	89	102	115
16 years	80	80	94	108	122

Why big dogs age faster

In most species, bigger animals live longer. Dogs are the exception: heavy breeds grow very fast and the signs of age (joints, heart, tiredness) arrive sooner. Hence 7 years per year for a giant dog against 4 for a small one.

Researchers have also suggested the formula 16 × ln(age) + 31, drawn from the DNA of dogs of a single breed: a research lead, not a rule. At 4 years it gives 16 × ln(4) + 31 = 53.18.

Life stages and care

The life stage follows the human-year figure: puppy or kitten under 15, young adult up to 40, adult up to 60, senior up to 75, geriatric beyond. A medium dog turns senior at 9 years and 3 months, a giant dog at 7 years and 2 months.

With age come more regular vet check-ups, food suited to the pet's age, and a closer eye on weight and mobility (stiffness when getting up, reluctance to jump into the car). For any health question, ask your vet.

Life expectancy

In broad ranges: a cat often lives 12 to 18 years, a small dog 12 to 16, a medium dog 10 to 14, a large dog 9 to 12 and a giant dog 7 to 10. Plenty of pets fall outside these ranges.

Frequently asked questions

My cat is 12. How old is that in human years?

24 + 4 × 10 = 64 human years: a senior, a stage cats reach at 11.

Which size for a mixed-breed dog?

The one matching its adult weight: 50 lb is "Medium", 70 lb is "Large".

Why is there a decimal?

Months count pro rata: a cat aged 1 year and 6 months is 15 + 9 × 6/12 = 19.5 in human years.

Is the logarithmic formula more accurate?

There is no way to say so. The calculator shows it for comparison, with the same warning.

Dog years calculator: dog and cat age in human years

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