Based on size, weight, and spay/neuter status.
Larger dogs age faster and have shorter lifespans — an inverse relationship unique among mammals. Small breeds (under 20 lbs): 12-16 years. Medium (20-50 lbs): 10-14 years. Large (50-90 lbs): 8-12 years. Giant (90+ lbs): 6-10 years. Spayed/neutered dogs live 0.5-1.5 years longer on average. Mixed breeds tend to outlive purebreds due to hybrid vigor. Factors that extend life: healthy weight, dental care, regular exercise, preventive vet care, and mental stimulation. The longest-lived dog on record was Bobi, a Rafeiro do Alentejo who reportedly lived 31 years. Common breeds: Chihuahua 14-16 yr, Lab 10-12, German Shepherd 9-13, Great Dane 7-10.