13 dog years in human years

≈ 79 human years for a medium breed. Size changes the answer a lot:

Small (under 20 lb / 9 kg)68 human years
Medium (21–50 lb / 10–23 kg)79 human years
Large (51–100 lb / 23–45 kg)90 human years
Giant (100 lb+ / 45 kg+)112 human years

At 13 years your dog is into senior territory for most breeds. Senior status starts around age 6 for giant breeds, 8 for large, 10 for medium and 11 for small ones — see the life stage chart.

Part-way through year 13 (medium breed)

13 yr 0 mo79 human years
13 yr 3 mo80 human years
13 yr 6 mo82 human years
13 yr 9 mo83 human years

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