Which column of the chart should I read?

Read the epigenetic column if you want the estimate that comes from a published measurement of molecular aging, and read your dog's size column if you want the practical, size-aware version vets use in conversation. They are two different methods and they will not agree; that disagreement is a fair summary of how approximate this whole exercise is.

Why does the chart stop at 20 years?

Because beyond twenty the numbers stop being useful. Very few dogs of any size reach that age, and the sample of dogs that do is too small and too unusual for either method to describe. Small breeds dominate the upper end of the chart in real life; giant breeds essentially never appear there.

Why are some cells a range instead of a single number?

Large-breed dogs are conventionally given about +5 to +6 human years per dog year after age two, and there is no principled reason to pick one end of that. Printing a single value — or worse, a decimal — would imply a precision that does not exist, so those cells show the honest range.

Can I use this chart for a mixed-breed dog?

Yes, using your dog's adult weight rather than its ancestry. A 25 kg mixed-breed dog is a large dog for the purposes of this chart, whatever the DNA test says. If your dog sits right on a boundary — around 22 kg, for example — read both adjacent columns and treat the two values as the plausible band.

Dog Years Chart: Dog Age to Human Age by Size

This is the complete conversion table behind the dog age calculator, from six months old to twenty years old. Each row gives two independent estimates: the epigenetic clock value, which ignores body size, and the veterinary rule of thumb, which is broken out by weight class because larger dogs age faster.

Dog age to human age. All values are whole human years and are estimates, not measurements.
Dog age	Epigenetic clock	Small under 9 kg (20 lb)	Medium 9-22 kg (20-50 lb)	Large 22-40 kg (50-90 lb)	Giant over 40 kg (90 lb)
6 months	~16*	8 Puppy	8 Puppy	8 Puppy	8 Puppy
1 year	31	15 Adult	15 Adult	15 Puppy	15 Puppy
2 years	42	24 Adult	24 Adult	24 Adult	24 Adult
3 years	49	28 Adult	29 Adult	29–30 Adult	31 Adult
4 years	53	32 Adult	34 Adult	34–36 Adult	38 Adult
5 years	57	36 Adult	39 Adult	39–42 Adult	45 Adult
6 years	60	40 Adult	44 Adult	44–48 Adult	52 Adult
7 years	62	44 Adult	49 Adult	49–54 Adult	59 Senior
8 years	64	48 Adult	54 Adult	54–60 Senior	66 Senior
9 years	66	52 Adult	59 Adult	59–66 Senior	73 Senior
10 years	68	56 Adult	64 Senior	64–72 Senior	80 Senior
11 years	69	60 Senior	69 Senior	69–78 Senior	87 Senior
12 years	71	64 Senior	74 Senior	74–84 Senior	94 Senior
13 years	72	68 Senior	79 Senior	79–90 Senior	101 Senior
14 years	73	72 Senior	84 Senior	84–96 Senior	108 Senior
15 years	74	76 Senior	89 Senior	89–102 Senior	115 Senior
16 years	75	80 Senior	94 Senior	94–108 Senior	122 Senior
17 years	76	84 Senior	99 Senior	99–114 Senior	129 Senior
18 years	77	88 Senior	104 Senior	104–120 Senior	136 Senior
19 years	78	92 Senior	109 Senior	109–126 Senior	143 Senior
20 years	79	96 Senior	114 Senior	114–132 Senior	150 Senior

* Below one year the epigenetic formula is undefined, so the value is interpolated linearly toward the one-year figure of 31 and should be treated as a rough approximation. Life-stage words next to each rule-of-thumb value follow the common size-based thresholds described on senior dog age.

How to read the chart

Find your dog's age in the left column, then read across. The epigenetic column comes from the formula 16 × ln(dog age) + 31, published in 2020 by UC San Diego researchers who compared DNA methylation patterns in Labrador retrievers and humans. It produces one number per age, because molecular aging in that study did not depend on body size.

The four size columns come from the clinical rule of thumb: about 15 human years for the first dog year, about 9 more for the second, and then a fixed annual increment that grows with body size — +4 for small dogs, +5 for medium, +5 to +6 for large, +7 for giant breeds. Pick the column that matches your dog's adult weight, not its current weight if it is still growing.

The pattern the chart makes visible

Three things stand out once you see the whole table at once. First, the first two rows move enormously and everything afterwards moves gently — dog aging front-loads. Second, the columns fan out with age: at two years old every size class reads the same 24, but by twelve years the gap between a small dog and a giant one is roughly 30 human years. Third, the epigenetic column starts far above the rule of thumb and is overtaken by the giant column at around eight years old, which is exactly the disagreement you would expect between a size-blind molecular measure and a size-aware clinical heuristic.

That fan-out is the reason the ×7 myth survives as long as it does: for a medium dog somewhere around six to eight years old, seven-times-age happens to land close to the rule of thumb. It is a broken clock being right twice a day, and it goes badly wrong for puppies, for very old dogs, and for anything much bigger or smaller than average.

Common ages people look up

1 year: the biggest single jump on the chart — roughly 15 human years by the rule of thumb, 31 by the epigenetic formula. Physically adult, behaviourally adolescent. More detail on puppy age in human years.
7 years: the age at which the "senior" label starts appearing for giant breeds while small dogs are still solidly middle-aged.
10 years: around 56 human years for a small dog, around 80 for a giant one — the clearest illustration on the chart of why size belongs in the calculation.
15+ years: almost exclusively small and medium dogs. The rule of thumb keeps adding years mechanically here, so treat the far end of the table as a rough scale rather than a claim.

Accuracy note

Everything above is an estimate. Neither method accounts for breed-specific disease risk, body condition, dental health, neuter status or the quality of veterinary care a dog has had, and all of those change how a dog actually ages. Use the chart to orient yourself, then ask your veterinarian about your specific dog. For the reasoning behind both methods, see how old is my dog in human years, or go straight to the calculator to enter an exact age in years and months.