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When Do Border Collies Stop Growing? [& Size At Maturity]

The border collie is a working and herding dog breed that was initially bred for herding livestock, particularly sheep. Naturally, they would need to be of a certain size to fulfill such a task. And while they are considered medium-sized dogs averaging 30 to 45 pounds in weight; how long does it take for them to get there? At what age can we expect them to reach maturity? Here is what you should know.

So, when do border collies stop growing? Border collies typically stop growing in height between 12 and 15 months of age. Although, they may continue to put on weight after 15 months – finishing their growth by around 18 months of age. It is worth mentioning that border collies do not behave like adult dogs until they are close to 24 months.

The border collie dog breed is one with what appears to be unlimited stamina and lots of energy.

These dogs were bred originally to herd sheep and still do to this day.

Border collies are highly intelligent dogs that are willing to please their owners; this makes them so easy to train.

Border collies do exceptionally well in different canine sports such as flyball, obedience, agility, and flying disc competitions.

But what about their overall size? Let us take a closer look and cover the topic in some more depth.

How Big Will My Border Collie Get?

The average male border collie will stand at 19 to 22 inches in height and weigh between 35 to 45 pounds.

Females are somewhat the smaller of the two sexes and stand at around 18 to 21 inches in height and weigh between 30 to 40 pounds.

For these dogs to grow healthy and robust, they require high-quality dog food; this is a must whether the food is commercially manufactured or home-made with your veterinarian’s instructions and approval.

Any diet you choose to offer your dog must suit your dog’s age.

You must monitor your dog’s calorie intake, and weight level as some dogs become overweight very quickly.

Border collies are medium-sized dogs, yet they are not suited to living in small spaces.

It is the nature of this breed to herd sheep, so they are incredibly active and require a home with lots of space indoors as well as outdoors to accommodate their energy levels.

These dogs are ideal for individuals or families who love to spend time with an active dog, whether indoors or outdoors.

Below is a handy weight chart by age, which you can typically observe in this breed:

Border Collie Weight Chart By Age

The table below includes information on how much your Border Collie (or most medium-sized dogs) will weigh at each milestone.

AgeWeight In Pounds (lbs)
8 weeks4.
9 weeks4.
10 weeks5.
11 weeks5.
12 weeks6.
13 weeks6.
14 weeks7.
15 weeks7.58.49.410.311.313.115.0
16 weeks8.
5 months11.012.413.815.116.519.322.0
6 months13.014.616.317.919.522.826.0
7 months15.016.918.820.622.526.330.0
8 months17.519.721.924.126.330.635.0
9 months19.521.924.426.829.334.139.0
10 months21.524.226.929.632.337.643.0
11 months24.
12 months26.029.332.535.839.045.552.0

If this table looks confusing; this is how to use it. You first need to look for a/your border collies age in the first left-hand column.

Then you can look for the average weights of border collies at this age.

From there, you scan downwards to see what size they will likely be at the numerous stages of their life.

For example – an 8-week old border collie pup can range from 4-8 pounds.

So, if you had an 8-week old border collie pup, and they were currently 6 pounds, you could expect them to be 9.8 pounds at 12 weeks, 19.5 pounds at 6 months and 39 pounds at 12 months.

Of course, these are just averages. Some dogs will be below or above the expectations – this will mostly depend on genetics, diet, and lifestyle.

However, they are close averages and give us a good idea of what to expect.

At What Age Is A Border Collie Fully Grown?

A border collie reaches its full-size between 12 to 15 months of age.

They continue to put on weight and reach their full weight by around 18 months of age.

Border Collies still behave immaturely until they are closer to 24 months – they start acting like adult dogs.

Between 16 months to 36 months, border collies often struggle to maintain a healthy weight, so having a balanced diet is key to their health.

Border collies are prone to specific health issues like epilepsy, hip dysplasia, and Collie Eye Anomaly.

Still, generally speaking, border collies are a healthy breed with a lifespan ranging from 10 to 17 years.

Factors That Influence Size And Growth Potential

Several factors influence the size and growth potential of your dog. Unsurprisingly, these factors are all related to health.

Border collies have some health issues that need monitoring and will, of course, impact your dog’s growth.

The average male border collie should be 19 to 22 inches tall and weigh 35 to 45 pounds when fully grown.

A female border collie should be 18 to 22 inches tall and weigh 30 to 40 pounds when fully grown.

Let’s explore some of the factors that would influence the size and growth potential of this breed:


Some border collies are prone to health complications such as epilepsy, hip dysplasia, and CEA.

Sometimes these genetic conditions are realized when the dogs are young, but this is not always the case.

Medical conditions may not be diagnosed until the dog matures. Health issues can impede your dog’s ability to exercise, which in turn can impact your pet’s potential size.


It isn’t enough to just feed our dogs enough food; we must provide them with fresh, high-quality food as nutrition impacts your dog’s development.

If your border collie is malnourished, it can cause health problems and lead to a lower quality of life.

It can mean they are less active and less able to exercise; which is of course critical to the well-being of this breed.

On the other side of the scale, dogs that are overfed can become obese, shortening your pet’s lifespan, due to the extra weight that they are carrying.

It will also lower the quality of their life, as they will likely experience joint issues from the additional pounds.

Border collies require a diet that is appropriate for their age and energy levels.

You can talk to your vet, who can guide you on nutrition. Always have enough fresh water for your dog, as being well hydrated is crucial for their health.


Border collies are working dogs and born to be sheepherders; they have very high energy levels and require adequate activity and exercise.

Strenuous daily exercise will help your border collie to grow healthy and strong. Aside from keeping your pet fit, exercise promotes good mental health for your dog.

It is worth mentioning that if your border collie is unwell or has an injury to go easy with exercise and perhaps find a fitness regime that is gentler and better suited to a sick or injured dog.


Border collies, like any pet, require a good life where they are loved and receive the right care.

Living a good life will help your pooch live long and healthy, and it will help your dog to reach his full potential physically as well as mentally.

If your border collie is a healthy dog, you must ensure he is getting enough exercise to keep them happy and stimulated.

These dogs require activity that is enriching and encourages a healthy lifestyle. Border collies are not to lie around all day; this will only bring stress into their lives.


Border collies make excellent pets for anyone who can keep up with them. These dogs are affectionate, child-friendly, and love to play.

However, you need to ensure that you have the time and energy for a border collie before bringing one to live with you.

They are lovely, loyal companions, but their energy levels necessitate lots of activity both indoors and outdoors.

Be aware that it takes time for border collies to behave like adults; it can take 24 months or more before they move out of their youthful phase.

Until these dogs reach maturity, life can be pretty chaotic but fun and memorable all the same.

Beyond this they are known to shed, so regular grooming is a must!

Related Questions

Are Border Collies Medium Or Large Dogs?

Border collies are classified as medium-sized dogs reaching up to 22 inches in height and 40 pounds in weight on average by 15 months of age. Officially, any dog breed over 50 pounds but under 100 pounds will be considered a large dog breed.

Are Border Collies Supposed To Be Skinny

Border collies are typically skinny and naturally lean; this is because they are a tremendously active and energetic breed. As such, keeping weight on a border collie can prove a challenge; even if they are fed handsomely. Particular foods, and talking to a vet is one of the best things you can do to ensure your border collie has sufficient weight and does not become or stay too skinny (whereby the rib cage becomes exposed and is visible).

When Do Border Collies Grow Long Hair?

Border Collies grow hair slowly, and it typically appears longer toward the end of puppyhood. It is around the five to seven-month age mark that longer hair is clearly visible. However, fur does appear to grow in different places in different areas of their bodies and to different lengths. Generally, growth of the mane, tail, and shirting become visible first while the fur on the remainder of the body continues to fill out until they reach an age of maturity. Some owners report that their border collie’s coat gets a little fuller with each passing year of age.

When Do Border Collies Calm Down?

A Border Collie will calm generally down during its latter years and the second half of its lifespan. Therefore, you can expect a calmer dog at around the 5-6 years of age mark. Of course, this will depend on the genetics of your collie, their environment, and how you take care of them. Border collies appear to take a while to calm down because they are very energetic and active dog breeds.