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When Do Border Collies Stop Growing?

If you have recently acquired a Border Collie puppy, you may be wondering how large your collie will get and how long it will take to reach its largest size.

Border Collies stop growing in length and height after 12-15 months, but they will gain weight until they are about 18 months, reaching a weight of between 30-45 lbs and a height between 18-22 inches. At about two years old, they will mentally mature and begin acting like full adult dogs.

To learn more specifics about the speed and arc of your Border Collie’s growth, as well as details about owning Border Collies in general, keep reading.

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Owning a Border Collie

Border Collies are widely known for being the most intelligent dog breed. This does not mean your Border Collie won’t be playful or get into trouble, but it does mean they can learn a lot of tricks and train very well! Their intelligence led them to become common sheepdogs, well-known for their ability to herd sheep successfully.

For some fascinating breed facts about Border Collies, check out this youtube video that provides insights into Border Collie ownership:

If you’ve had a Border Collie for a while, you probably know this is an energetic breed with high stamina, making them perfect for long days herding sheep or playing.

While this energy can be fun, it also means your Border Collie may require more walks and playtime than other dogs. You should walk your Border Collie multiple times per day, and ensure they have plenty of playtime so they can develop proper muscles and shapes.

Furthermore, your Border Collie should not live in a small space; they need plenty of room to move and run. Therefore, if you live in an apartment, a Border Collie is probably not the right dog for you.

Border Collies have perky ears that enable them to hear far and long fur coats. Long fur prevents them from being hypoallergenic, but they generally do not shed too much, especially with the right grooming and dog food.

One vital aspect of a collies’ ability to mature is socialization. Border Collies that spend a lot of time alone may grow up to be less social and less interested in other dogs, while Border Collies exposed to many people and dogs as puppies will be more friendly to other dogs as they age.

Your Border Collie may live from 10 to 17 years if they do not have any severe medical issues, but will only grow in height for about the first 18 months of their life. Overall, Border Collies are classified as medium-sized dogs that do not reach large sizes.

One aspect of Border Collies’ growth that is often overlooked is its fur. As puppies, Border Collies do not typically have long fur, and their fur will usually grow out as they age.

Generally, Border Collie fur reaches a typical length by the time they reach emotional maturity, but some dog owners say their collie’s fur continues to thicken every year. Longer fur may contribute to slight weight gain and a larger appearance, but this is quite normal for long-haired dogs.

As a Border Collie owner, you will enjoy a warm, energetic, and intelligent dog that keeps you busy with walks and affection. However, when your dog is a young puppy and full of energy, you may be exhausted by the constant energy and weight fluctuations they have and feel ready for them to reach physical and mental maturity.

How Big Do Border Collies Get?

As mentioned, Border Collies are medium-sized dogs. Any dog that reaches over 50 pounds (23kg) is considered a large dog, so while some collies are borderline, most will stay in the medium range.

Like any dog, Border Collies go through developmental phases as they grow. During these phases, your Border Collie’s height, length, and personality may shift. Your Border Collie should gain weight continuously for at least the first year of its life.

On average, Border Collies may weigh between 25-50 pounds (11.3-23kg), but this depends on factors such as gender and breeding. Usually, females will reach 18 to 21 inches in height and 30 to 40 pounds (14-18.1kg), while males are 19 to 22 inches and 35 to 45 pounds (16-20.4kg).

First Six Weeks

For the first six weeks of its life, a Border Collie puppy should gain at least ½-1 ½ oz per day. Then, from 8 to 16 weeks, they will gain about half a pound per day, reaching between 8 and 16 pounds. If your Border Collie is outside this range, don’t worry- every dog is different, and what is most important is that your dog grows steadily relative to their original weight, not that they are in a specific range.

First Year

From 5 months to a year, your Border Collie will gain about 2-3 pounds each month. For example, if your collie is 15 pounds (7kg) when they are five months old, they could be 35-36 pounds (16kg) when they reach a year.

This is an average weight for a collie and may signify that they are finished growing, but if your collie continues to gain weight for the next few months, that is okay!

How to Approximate How Big a Border Collie Will Get

Luckily, there is a simple way to approximate how large your Border Collie will get if you are unsure. Since their maximum size is relative to their size in the first few weeks and months of their life, you can make a guess as to how much they will grow by using their current weight.

To guess your dog’s adult weight, you can make a calculation using their current weight by their age in weeks, then multiplying that number by 50-52, which is likely the largest your collie will become. This calculation basically uses your dog’s current size to determine how big they will be by comparing them to the largest dog.

For example, if your puppy is 9 pounds (4kg) at 14 weeks, you would divide nine by 14 to get .64. Then, you would multiply .64 to get about 32 pounds (15kg), meaning your Border Collie should stop growing when they are approximately 32 pounds. This formula is not exact, but it is a good way to estimate how much more your Border Collie will grow before it reaches full size.

The most rapid phase of a Border Collie’s growth occurs from 3 to 6 months. When your collie is between 16 and 36 months, it will complete its physical and emotional transition into adulthood. However, even when it is not a puppy, your collie will still be playful, energetic, and fun-loving throughout its life.

Border Collies are a very loyal breed and will stand by your side throughout their lives. When they finish growing, they are a beautiful, medium-sized dog that makes the perfect size for any family.


Usually, Border Collies stop growing in height after 12 to 15 months and gain weight until they reach 18 months. This weight relies on factors such as your dog’s gender, feeding, and activity level. However, they may not reach emotional maturity until they are about 2 to 3 years old, and experience fur growth into their later years of life.

If you are considering a Border Collie or have recently acquired a puppy, be ready for an energetic, enthusiastic puppy that will maintain this energy throughout its life. As a Border Collie owner, you will find a deeply loyal and loving companion who will stay by your side regardless of their size.