Dog Age Calculator: Dog Years to Human Years (by Size)

How it works

How to use the dog age calculator

Type your dog's age in years and months, or pick the birthday if you know it.
Choose the size band that matches your dog's adult weight. Large dogs age faster in the second half of life, so this changes the answer.
Read the headline number (the AAHA size chart), then compare it with the UCSD and AVMA figures underneath.
Add an expected lifespan from your vet if you want the year the senior stage starts.

All results are estimates. No single formula fits every breed, and the tool does not diagnose anything.

Methods compared

Three ways to convert dog years, and where they disagree

The old rule says one dog year equals seven human years. It is easy to remember and wrong at both ends of life: a one-year-old dog is far closer to a teenager than to a seven-year-old child. The calculator therefore shows three better-founded numbers.

AAHA size chart (headline)

The American Animal Hospital Association chart used by many veterinary practices gives different values for small, medium, large and giant dogs. It starts at 15 human years at age 1 and 24 at age 2 for every size, then diverges. By age 10 it gives 56 for a small dog and 78 for a giant.

UCSD Labrador formula

Researchers at UC San Diego measured DNA methylation in 104 Labrador retrievers and fitted human age = 16 x ln(dog age) + 31. It puts a 1-year-old dog near 31 human years and a 4-year-old near 53. It was built on one breed, so treat it as a research reference, not a rule for every dog.

AVMA rule of thumb

The AVMA guidance for a medium dog (21 to 50 lb) counts the first year as 15 human years, the second as 9 and every year after as about 5. Because it ignores size, it runs a little high for small dogs and low for giants.

Old 7x rule

Shown only so you can see the gap. At age 1 it says 7 against about 15 to 31 in the sources above; at age 15 it says 105 against 76 to 115 depending on size.

Dog age	Small	Medium	Large	Giant	UCSD (Labrador)	Old 7x rule
1	15	15	15	15	31	7
2	24	24	24	24	42	14
3	28	28	29	30	49	21
4	32	33	35	36	53	28
5	36	37	40	42	57	35
6	40	42	45	49	60	42
7	44	46	50	56	62	49
8	48	51	56	64	64	56
9	52	55	61	71	66	63
10	56	60	66	78	68	70
11	60	65	71	85	69	77
12	64	69	77	93	71	84
13	68	74	82	100	72	91
14	72	78	88	108	73	98
15	76	83	93	115	74	105
16	80	87	98	-	75	112
18	88	96	109	-	77	126
20	96	105	120	-	79	140

Human-year equivalents. Small to giant columns are interpolated between the AAHA chart values at 1, 2, 5, 10, 15 and 20 years; the UCSD column is 16 x ln(age) + 31.

Life stages

What your dog's age means for care

AAHA's 2019 canine life stage guidelines define stages by development rather than by a fixed age:

Stage	Definition (AAHA 2019)
Puppy	Birth to the end of rapid growth, roughly 6 to 9 months depending on breed and size
Young adult	End of rapid growth to full physical and social maturity, reached by most dogs at 3 to 4 years
Mature adult	From maturity until the last 25% of the dog's estimated lifespan
Senior	The last 25% of estimated lifespan, which depends on breed and size

That last row is why the calculator asks for an expected lifespan: a giant breed expected to live 9 years is senior at about 6.75, while a small dog expected to live 15 years is senior at about 11. AAHA deliberately gives no fixed age for the mature and senior stages because the spread gets wider with age. Ask your vet what applies to your dog, and see our vaccination schedule for what to book at each stage.

Go deeper

Why size changes the answer

Large and giant dogs have shorter lives, so each calendar year uses up more of it. The AAHA chart captures that: by age 15 a giant dog sits at 115 human years against 76 for a small dog. The UCSD study is a reminder that the maths behind this is still being worked out. Its authors say studying breeds with other lifespans would show whether the clock holds beyond Labradors.

Want a feel for how a puppy is growing rather than ageing? Use our puppy weight calculator, or read the puppy growth chart guide. Cat owner? The cat age chart uses a different curve.

From Reddit

What owners ask on Reddit

Quotes are copied word for word from public Reddit threads. They are single people's accounts, not evidence, and we use them only to show the questions the tool is meant to answer.

“it's possible to have a 5 year old dog who happens to have really good teeth, and it's possible to have a 2 year old dog with really bad teeth (and a vet might guess those two dogs to be the same age).”

r/dogs, Sep 2026, a thread about a rescue dog of unknown age · Reddit thread

Our take. The calculator needs an age, so for a rescue enter the low and high end of the vet's estimate one after the other and read both. On the AAHA chart a medium dog is 15 human years at 1 and 24 at 2, so a wrong guess of a year moves the answer by about nine.

“Mine was off by about 4 months on my rescue, but I adopted her from shelter so who knows if the birthday they gave me was even correct in first place.”

r/DoggyDNA, Oct 2026, owners comparing dog age tests · Reddit thread

Our take. A birthday that came from a shelter may itself be a guess, and one owner's result says nothing about how accurate a test is in general. Treat any age you did not record yourself as a range, and use the senior-stage line in the tool as a prompt to ask your vet, not as a deadline.

Questions

Frequently asked questions

How old is my dog in human years?

Enter the age and size above. As a guide, a medium dog is about 15 human years at 1, 24 at 2, 37 at 5 and 60 at 10 on the AAHA chart. Small dogs are younger at the same age and giant dogs older.

Is one dog year really seven human years?

No. Dogs mature far faster in the first two years, then age more slowly. The AAHA chart and the UCSD study both disagree with a flat multiplier of seven.

Why does size matter?

Larger dogs tend to have shorter lifespans, so each year is a bigger share of their life. Chart values for the same age diverge after year two: at 10 years it is 56 for small and 78 for giant.

Which method is the most accurate?

None is exact. The AAHA chart is the most practical because it accounts for size. The UCSD formula is the most scientific but was fitted to Labradors only. Use them as a range.

When is my dog a senior?

AAHA defines senior as the last 25% of a dog's expected lifespan, which varies with breed and size. If your vet expects 12 years, senior starts near 9.

Does this work for mixed breeds?

Yes. Pick the size band for your dog's adult weight. If you are unsure, use the medium column and read it as a midpoint.

Can I use it for puppies?

Under one year the chart has no values, so the tool shows a straight-line estimate of 15 human years per dog year. Puppies grow very fast, so treat it loosely.

Keep going

More tools for your pet

ToolCat age calculatorCat years in human years, with the vet-recommended curve.ToolPuppy weight calculatorPredict adult weight from your puppy's weight today.ToolDog food calculatorDaily calories and cups for your dog's age and weight.

Sources

Where the numbers come from

AAHA canine life stage guidelines (2019) — puppy, young adult, mature adult and senior definitions
Chewy, Dog Years to Human Years (updated Feb 12, 2026) — reproduces the AAHA size-band chart and the AVMA medium-dog rule; our small-to-giant values are interpolated from the chart rows at ages 1, 2, 5, 10, 15 and 20
UC San Diego news, 2020 — Labrador epigenetic clock, Wang et al., Cell Systems
Sci.News summary of the Cell Systems study — the 16 x ln(age) + 31 formula and the one-breed limitation

This calculator is for general information and does not replace veterinary advice. Last reviewed October 2026.

Dog Age Calculator: Dog Years to Human Years