Dog Age Calculator: Dog Years to Human Years

There is no single, exact way to turn a dog’s age into human years. Veterinary sources use a size-based chart, and a 2020 study from the University of California San Diego proposed a formula based on DNA changes. This calculator shows both, because they often disagree, and the difference is useful to understand.

Method 1: the size-based chart

A widely quoted size-based chart is published by the American Kennel Club (AKC), with four columns by adult weight. The American Veterinary Medical Association (AVMA) publishes the same values for a medium-sized dog of 21–50 lb. As the AKC summarizes the AVMA guideline:

• the first year of a medium-sized dog’s life equals about 15 human years;
• the second year adds about 9 (so a 2-year-old is about 24);
• after that, each dog year counts as roughly 5 human years for a medium dog, fewer for small dogs and more for large and giant dogs.

The calculator reads your dog’s value from the table below. For ages between whole years (for example 6 years and 6 months) it takes the point on a straight line between the two neighboring years.

Dog age	Small (≤20 lb)	Medium (21–50 lb)	Large (51–100 lb)	Giant (>100 lb)
1	15	15	15	12
2	24	24	24	22
3	28	28	28	31
4	32	32	32	38
5	36	36	36	45
6	40	42	45	49
7	44	47	50	56
8	48	51	55	64
9	52	56	61	71
10	56	60	66	79
11	60	65	72	86
12	64	69	77	93
13	68	74	82	100
14	72	78	88	107
15	76	83	93	114
16	80	87	99	121

Human-year equivalents. Source: AKC dog age chart; the medium column matches the AVMA “Pets age faster than people” poster.

Notice the pattern: up to age 5 the small, medium and large columns are identical. After that they spread apart, because larger dogs tend to have shorter lives. Giant breeds start lower (12 at one year) but quickly overtake every other column.

Method 2: the epigenetic formula (UCSD, 2020)

In 2020, researchers led by Tina Wang and Trey Ideker at UC San Diego published a study in Cell Systems comparing chemical marks on DNA (methylation) that change predictably with age in both dogs and humans. They studied 104 dogs, mostly Labrador retrievers, and matched them against human data. Their conversion is:

human age = 16 × ln(dog age) + 31

where ln is the natural logarithm and the dog’s age is in years. The formula changes fast early in life and slowly later:

Dog age	Epigenetic formula (human years)
1	31
2	42.1
4	53.2
7	62.1
10	67.8
12	70.8
14	73.2
16	75.4

Worked examples

Example 1: a 7-year-old medium dog (say, 40 lb). Chart: read the medium column at 7 → 47 human years. Formula: 16 × ln(7) + 31 = 16 × 1.946 + 31 = 62.1 human years. The formula makes a young-ish adult dog look much older than the chart does.

Example 2: a 6½-year-old large dog (say, 75 lb). Chart: between 45 (age 6) and 50 (age 7), halfway → 47.5 human years.

Example 3: a 10-year-old small dog vs. a 10-year-old giant dog. Chart: small column → 56, giant column → 79. The formula gives 67.8 for both, because it doesn’t consider size.

Example 4: a 2-year-old dog. Chart: 24 for small, medium and large dogs. Formula: 16 × ln(2) + 31 = 42.1.

Why the two methods disagree

• Different questions. The chart compares stages of life (growth, maturity, old age) across dog sizes. The formula compares a molecular “clock” in blood cells.
• Size. The chart has four size columns. The formula was built on one breed, the Labrador retriever, and the authors note that breeds with different lifespans could need different conversions. UC San Diego’s own news release calls the single-breed design a limitation.
• Early vs. late life. The formula rises steeply in the first years (a 1-year-old is already 31) and flattens later (a 16-year-old is only 75). The chart rises more evenly.

Neither method tells you how healthy your dog is. A 10-year-old dog in good condition and one with chronic disease get the same number.

Limitations

• The chart’s values are a convention. Neither the AKC page nor the AVMA poster explains how each value was derived.
• The epigenetic study used blood samples, mostly from Labradors. Results for very small, very large or mixed-breed dogs, and for very young puppies, are less certain.
• Lifespans vary a lot by breed and individual. If you want to know whether your dog’s age calls for senior check-ups, ask your veterinarian.