Canine Life Stage Definitions

For practical purposes, rather than attempt to calculate age equivalents to humans, the task force suggests that life stage be defined both by age and characteristics. Life stage divisions, although arbitrary, provide a framework for creating individualized plans for preventive care specific to each dog’s needs at the appropriate time. Table 1 (below) provides broad-based definitions of the four life stages used in these guidelines.

Table 1: Proposed Canine Life Stage Definitions



From birth to cessation of rapid growth (~6–9 months, varying with breed and size)

Young adult

From cessation of rapid growth to completion of physical and social maturation, which occurs in most dogs by 3 to 4 years of age

Mature adult

From completion of physical and social maturation until the last 25% of estimated lifespan (breed and size dependent)


From the last 25% of estimated lifespan through end-of-life.


The terminal stage (depends on the specific pathologies)

These guidelines focus on life stages that require different approaches to preventive care. The spectrum of care within each life stage is affected by the age, size, lifestyle, health status, and breed of the dog.3–5 Physiological and behavioral developmental periods do not start and end abruptly, but phase in and out gradually. Within each life stage category there will also be variation that demands clinical judgement. Because variation increases toward the latter years, estimates of inclusive ages are not uniform and therefore are not proposed for the life stages of mature adults and seniors. Estimation by the practice team of an individual dog’s lifespan, generally predicted by breed lifespan, permits more accurate targeting of life stage–specific preventive care.6 The Canine Life Stage Checklist provides a checklist of items to discuss with each pet owner based on life stage. This table of additional resources offers suggestions to help predict longevity in various common breeds.

The 2019 AAHA Canine Life Stage Guidelines are supported by generous educational grants from Boehringer Ingelheim Animal Health USA Inc., CareCredit, Elanco Animal Health, Hill’s ® Pet Nutrition, Inc., IDEXX Laboratories, Inc., Merck Animal Health and Zoetis Petcare.