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Dog Age in Human Years by Breed Size

Convert your dog’s age to human years using its breed size — small, medium, large or giant dogs age at different rates than the old “times 7” rule.

Dog’s age

Breed size

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How it works

first year ≈ 15 human years · second year adds ≈ 9 (so age 2 ≈ 24) · each year after age 2 adds ~4 (small), ~5 (medium), ~6 (large) or ~7 (giant) human years

The old “multiply by seven” rule is misleading because dogs mature very fast early on and then age at a pace that depends on their size. Most reference charts put the first year at about 15 human years and the second at another nine, reaching roughly 24 by age two. After that, small breeds age slowly (about four human years each), while giant breeds age quickly (about seven), which is why large dogs have shorter lifespans. This calculator applies that size-based rate to give a more realistic figure than a single multiplier.

Worked example

A 5-year-old medium dog: 24 human years at age two, plus 3 more dog years at about 5 each, gives 24 + 15 = 39 human years. The same age in a giant breed comes to 24 + 3×7 = 45.

Frequently asked questions

Why does breed size change the answer?

Small dogs live longer and age more slowly in their later years, while giant breeds age fast and have shorter lifespans. Applying a size-specific rate after age two reflects this far better than one universal multiplier.

Is the “times 7” rule wrong?

It is a rough oversimplification. Dogs reach the equivalent of the mid-teens in their first year alone, so multiplying by seven understates a young dog’s maturity and ignores the big differences between breed sizes.

How accurate is this?

It follows widely published veterinary charts and is a good general guide, but individual dogs vary with genetics, weight and health. For a science-based single figure, some researchers use a logarithmic formula derived from DNA methylation; this size-based chart is easier and close for most pets.

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This calculator is for educational purposes. Double-check important results before acting on them.