At What Age Is a Dog Fully Grown?


Quick Answer

Most dogs reach their full adult height and weight by 2 years old, although this varies depending on the breed of the dog. Giant breeds like mastiffs and Great Danes are an exception. They generally reach the majority of their height by about 18 months and continue to fill out thereafter. Giant breeds reach their adult weight by 3 years of age.

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Full Answer

Small and toy breeds tend to mature faster and usually stop growing at 10 months to 1 year old. Most medium-to-large breeds, including popular pet breeds like Labrador retrievers, stop growing in height at around 18 months but continue to develop deeper chests and more muscle, causing them to gain weight past 18 months. The last growth plates close at about 375 days, or just over one year, on average, but this depends on the individual animal and the breed.

Early spaying or neutering may also affect the dog's growth rate. Some of the later growth involves developing secondary sexual characteristics, such as a deeper chest and broader head, neck and shoulders in male dogs. Early neutering may reduce or prevent this, allowing the dog to reach adult weight faster. There is also some evidence that early neutering may delay growth plate closure, which may not translate to increased height but increases the risk of bone fractures during heavy exercise due to the immature skeletal structure. However, there are limited studies in this area, and many veterinarians believe the behavioral benefits of early neutering outweigh the risks.

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