When Do Border Collies Stop Growing?

By John Martin - August 11, 2022

Growing border collie puppy playing in the grass

Have you almost decided on getting a Border Collie and still have a few questions…such as how big do they get, what age do they stop growing, etc.? This article covers that and much more to give you a better idea of what you can expect that puppy to grow up to be.

We cover the basics of Border Collies, growth cycles, ideal size you can expect and even some things you need to be aware of that can affect the growth rate of your Border Collie.

Border Collie Breed Basics 

Let’s first get a little bit of an overview of this wonderful breed. They were initially sheepdogs that were bred to herd livestock and cattle near the borders of Scotland. 

People do still use them to herd, but they are also wonderful to show dogs, great at canine sports, and generally great companions thanks to their superior intelligence.

Border Collies’ bodies are slightly longer than they are taller. They have perked ears with droopy tips. Most Border Collies come in black and white, but nowadays, you’ll find them in so many more colors.

Border Collies are a highly energetic breed and are suited to families who spend a lot of time with their dog, whether it’s indoors or outdoors. They also need the right amount of exercise to spend their energy.

They are generally a very healthy breed, with an average lifespan of around 17 years. However, some specimens are prone to health issues like epilepsy, hip dysplasia, and Collie Eye Anomaly.

Related: Are Border Collies Good With Cats?

Growth Cycle of Border Collies

To get an understanding of the life and development of the Border Collie and to understand when it actually stops growing, let’s have a look at the growth cycle of this breed. 

The crucial thing to keep in mind is that every puppy grows at its own rate. Whether they are from the same breed or not, development is unique to each and every puppy.

The only important thing to keep track of is whether they are gaining weight steadily or not. This is the best indicator of growth and development in any puppy of any breed.

Neonatal Period 

From Birth to 3 weeks 

The average weight of a newborn Border Collie pup is around 7-14 ounces. During the first 24 hours of their life, you may witness a little bit of a loss through water weight.

After this, they need to immediately begin to gain weight. From the first week to six weeks, ideally, the puppy should be doubling in weight. This should be somewhere around 0.5-1.5 ounces a day.

During this stage, Border Collie pups cross their first milestones, such as opening their eyes, crawling slowly, and developing their very first set of baby teeth.

Socialization Period 

From 3 weeks to 12 weeks 

By the sixth week, the Border Collie puppy should weigh in at around 3-6 pounds. This is usually a four-time increase in their weight.

Although they are highly active puppies, they are still expected to gain around 2-4 pounds per week right up until the 14th week. 

At this stage, Border Collie puppies begin to socialize. This is not limited to their mother and siblings. They begin to interact a lot with their surroundings. 

At this stage, it is still better for the puppies to be with their mom since they learn social skills from their mother. However, this is also the stage where they should be introduced to new sights, sounds, and smells.

Juvenile Period 

From 3 months to 6 months 

At 14 weeks, the extremely rapid increase in weight begins to slow down. Weight gain is probably limited to around a pound a week until they reach six months of age.

During this adolescence period, Border Collie pups are very hungry. They eat a lot of food, as they need to support their high energy and metabolism levels. 

At this stage, all their baby teeth start to transition to adult teeth, and their motor skills begin to develop at a very rapid rate.

Sexual Maturity Period 

From 16 months to 36 months 

Once the teenage stage is completed, an adult Border Collie will have reached a more consistent weight that should not constantly be fluctuating.

Although there are no more significant growth milestones left by this stage, Border Collies will continue to grow. Around now, they start to reach their full-sized frames. They will continue to fill them out.

Female Border Collies are considered adults at the age of 24 months, while male Border Collies reach adulthood only by 36 months of age. 

So, in essence, Border Collies stop growing at around 12 to 15 months. They will continue to gain weight until 18 months of age. Once they reach 18 months, they are at their full size.

Although they reach their full adult size at 18 months, Border Collies are very playful, inquisitive dogs who may not act like adults until they reach about 24 months of age. 

What’s the Ideal Size for Adult Border Collies? 

The typical male Border Collie will weigh in at around 35-45 pounds, standing at the height of 19-22 inches.

The typical female Border Collie will weigh in at around 30-40 pounds, standing at the height of 18-22 inches.

Now, let’s look at some of the factors that affect the size and growth of Border Collies: 


As mentioned before, some specimens of this breed are prone to certain health issues. While it is always best if any health issues are diagnosed at an early age, it may not always be the case. 

Health issues and another generic coding within the dog tends to have an impact on the rate of growth, weight gain, and eventual size in Border Collies.


When it comes to feeding pets, it needs to be just right. There can be no wiggle room on either side of the marker. Too much is not good, and too little is also not good for them.

Border Collies that are fed too much will get overweight. While this weight gain may seem healthy at first, their joints are undergoing more stress, and their lifespan is reducing.

Malnourished Border Collies will definitely not reach their full growth potential. They need the right amount of nutrition and food intake to grow to their full size. 

Border Collies need to be fed a very precise diet that varies with their age and energy levels. They need to be given enough water, as they need to be hydrated to stay healthy.


As you now know, Border Collies were born to be cattle herders and worker dogs. This means that they have very high energy levels.

Border Collies need to be exercised regularly and rigorously so that they can continue to grow strong and healthy. Apart from fitness, exercise also helps promote good mental health in Border Collies.


Like any other breed, Border Collies require a lot of love and attention to keep them happy and comfortable. They must be getting enough exercise and socialization to stay mentally healthy. 

Border Collies are a very active and social breed. Lying around, not doing anything all day, and not having anyone to play with or meet will lead to them developing high levels of stress.

This can negatively impact its growth rate.

General Behavioural Traits of Border Collies

Border Collies are an excellent breed of dog. Highly intelligent, sociable, and hardworking. They are excellent with children and work beautifully as a family pet.

While saying that, it’s also important that those who wish to have a Border Collie must have the time and energy to keep up with a Border Collie.

Their high energy levels mean that they need to spend a lot of time involved in some activity or the other. This could be indoors or outdoors.

Border Collies are creatures of habit. They like to fall into a daily routine and like to follow it fastidiously. They are very intelligent dogs, so they will notice any small changes to their daily routine. 

This can confuse them and cause them to get upset. It’s best to set a particular routine for Border Collies from a young age and continue that routine well into their adulthood.

Border Collies must have obedience training from a very young age. Due to their high energy levels, Border Collies that aren’t trained in obedience will become very difficult to keep at home. 

They must be trained to sit, stand, and stop barking on command. This is especially helpful when the owners have guests at home. They are inquisitive dogs, so they may want to investigate new people.

Not all people are dog lovers, so Border Collies need to be trained to stay away from guests if you give them the command. They are quick learners, so they usually pick it up well. 

Another thing to remember about Border Collies is their attention span. Due to their higher intelligence levels, it is common for these dogs to have wavering attention spans. 

The owner of the dog must always ensure that they have the dog’s complete attention while attempting to teach or train the dog in any way. This ensures the retention of learning.

As mentioned before, these dogs don’t start to behave like adult dogs until they reach 24 months of age. So until that happens, life with Border Collies can be chaotic and hectic, but a massive load of fun. 

Training Border Collies 

Although they are very quick, intelligent learners, it is said to be ideal to wait till around 7-8 months to begin training Border Collies. You have a good 16 months till adulthood to train them and teach them new things. 

A high level of intensity is very common among Border Collies. They are always willing to learn and looking to learn something new. Border Collies excel at repetition, so they can fall into a rhythm easily. 

Border Collies are only concerned about completing the task at hand, so weather and the conditions surrounding them aren’t much of a deterrent to them at all. 

If there’s something that a Border Collie wants to be done, they will go through rain, shine, mud, and sleet to get it done. They have the ‘run through a brick wall’ attitude to any task set to them.

So there you have it. A comprehensive overview of Border Collies. They become full adults between the ages of 24-36 months and stop growing physically at around the 18-month mark.

Border Collies are an example of a wonderful domestic breed. They have so much love and adulation for their owners and will do absolutely anything to gain their owners’ love and respect.

For those planning to get a Border Collie, just remember. They are balls of energy and need to be appropriately loved, exercised, and trained to make sure they stay healthy and happy.