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When Do Border Collies Stop Growing: (Full Growth Guide)

Border collie owners soon start wondering when their pup will finally stop growing and reach their full adult size. This article covers everything there is to know about the border collie growth timeline.

In general, border collies stop growing by 2 years of age. Female border collies stop growing around 15-18 months of age whereas males stop growing around 18-24 months of age. Full height is always reached much sooner than full weight.


When Do Border Collies Reach Their Full Size

Although it seems like your pup will keep growing forever, they will reach their full size quicker than you think! Trust me, I know the feeling.


Border collies both male and female typically reach their full height around 12-15 months of age. Some may be a little earlier but rarely do any take longer than 15 months to reach their maximum height.


Weight, however, continues to pile on slowly in the form of muscle until around 15-18 months for the females and up to 24 months for large males.

It’s always important to remember that overall size is comprised of both height and weight, and your collie will reach her adult height a long time before she will reach her adult weight.

Related: Key differences between male and female border collies

How Big Do Border Collies Get?

Let’s run through the average adult size ranges you can expect your collie to fall between.

The average size for adult MALE border collies:
Height: 19-22 Inches
Weight: 35-50 Pounds (15-22 kg)

The average size for adult FEMALE border collies:
Height: 18-21 Inches
Weight: 30-40 Pounds (13-18 kg)

These are the most common averages that the majority of adult collies fall between.

Of course, there are always exceptions and some border collies might end up being smaller or larger than the breed standard.

Border Collie Growth Timeline

Growth timelines can be very helpful, but at the same time, it’s important not to get too fixated on them. For example, I’ve had many friends call unnecessary vet visits just because their pup didn’t match up to the exact weight they read online.

Just like in the last section, growth timelines are created from averages, so if your pup isn’t absolutely spot on, it’s likely nothing to worry about (as long as the difference is too drastic).

As weight is the most essential measurable growth factor, height is not included in the following chart.

Age (months)Male (pounds lbs)Female (pounds lbs)
18-2435-50 (min + max)30-40 (min + max)

Are Border Collies Considered Medium or Large Dogs?

Although border collies are technically considered medium-sized dogs by the American Kennel Club, some collies can indeed grow to be particularly large and appear to onlookers as a “large” dog.

Having said that, most collies will look like medium-sized dogs, and you’ll see a clear difference in size when compared to an adult German shepherd, Doberman, or Irish setter (for example).

Medium dogs usually range from 18-22 Inches in height compared to large dogs that range from 23-27 Inches in height.

What Age Do Border Collies Mature?

Many owners desperately want to know when their border collie pup will mature into a sensible adult.

Sexual maturity:

In terms of sexual maturity, a female border collie usually experiences her first heat cycle between 6-12 months of age, and from this moment, will be considered sexually mature as she’s capable of reproducing.

Most males tend to reach sexual maturity around seven months of age or in some cases, a few months later.

Mental maturity:

Female collies tend to mature mentally a little earlier than males, but in general, it takes around 2 years before a border collie (male or female) is considered mentally mature.

Keep in mind there is no set moment for this kind of maturity, and it will vary for each collie. Additionally, mental maturity doesn’t mean a sudden change of behavior or calming down (so don’t rely on age alone for that one!)

Recommended Read: 9 Best Ways To Keep Your Border Collie Cool In Summer

4 Factors Affecting The Size of Border Collies

There are a handful of factors that affect the size potential and growth rate of your border collie. Let’s take a look at them below.

1. Genetics

Of course, the most influential factor in your collie’s overall growth is her genetics. And you guessed it, there’s nothing we can do to “adjust” this.

If your collie is from a family of particularly large collies, then there’s a strong chance your collie will naturally grow to be bigger as well. On the other hand, if the parents of your collie puppy are on the smaller side, there a strong chance your collie will also grow to be on the low end of the size range.

2. Diet & Nutrition

The quality of the diet and nutrition your collie receives while she’s growing rapidly between 3-10 months can have an impact on size potential.

If your pup doesn’t receive sufficient protein, fats, calories, and micronutrients such as vitamins and minerals, then it’s possible her growth could be affected negatively. At least in the short term.

Puppies should only be consuming food from reputable brands that have tailor-made the formula for puppies. Avoid “all-life stages” as they don’t take into account a puppy’s higher nutritional requirements.

Once more, it’s crucial that your puppy actually gets on well with the food. Even if you’re using a high-quality kibble on paper, this doesn’t mean anything if your collie has a particular intolerance to it. Any intolerances will likely lead to mal-digestion or mal-absorption of the nutrients.

As diet and nutrition is a complicated topic, if you’re unsure, it’s best to consult your veterinarian. They will assist you with a diet plan made specifically for your pup.

3. Rest & recovery

There’s a reason why puppies sleep 16-20 hours a day! This is when they do the vast majority of their growing.

Ensuring your puppy has high-quality rest periods, without interruptions is going to be important for her overall growth and development.

There isn’t anything for you to do here as long as you provide your pup with a comfy bed, they will sleep when needed.

For households that have young children, it will need to be addressed to them that they must let the puppy rest, and waking them up from napping or sleeping isn’t allowed.

4. Careful exercise

It’s so important to avoid over-exercising yet it is still necessary to provide exercise… And this can be hard to get our heads around, especially when they appear to be physically capable.

The safest way to exercise your collie puppy is to follow the 5-minute method. This means providing 5 minutes of dedicated exercise per day, per month of age they are. So at 3 months old, they receive 15 minutes per day, at 4 months, 20 minutes per day, and so on.

The 5-minute method is a veterinarian-approved exercise plan that border collie owners should ideally follow. The slow, gradual increase in exercise will ensure your pup receives sufficient muscle stimulation, yet it will prevent you from accidentally providing too much exercise. It’s best to follow this until around 10-12 months of age.

Do this at the start of every day so you know you have covered her “dedicated exercise.” All other playing around within the home after this is completely fine, although your pup should still avoid excessive jumping and chasing.

Recommended Read: 8 Ways To Keep Your Border Collie Mentally Stimulated

Border Collie Size & Growth FAQs

This section will cover the more specific frequently asked questions and provide a short and concise answer.

What age is a border collie fully grown?

Border collies are considered fully grown by 18-24 months of age. By this time, collies usually stop filling out and putting on muscle, and they would have already reached their full height a long time before this.

How tall will a male border collie get?

Male border collies typically grow to be 19-22 Inches in height. These are averages, however, and not all males will fit perfectly within this range, few will be shorter or even taller in rare cases.

Why is my border collie puppy so small?

It’s normal for owners to consider their puppy to be smaller than average. It’s important to keep in mind that it takes a long time for a collie to fill out, so it could just be a time factor. However, if your pup is drastically underweight, a vet appointment should be your priority.

Can I do anything to make my border collie bigger?

Overall size comes mostly down to genetics, which we can’t do anything about. But for your collie to reach their full potential it’s important to feed a high-quality nutritious diet as well as allow adequate rest but also the right amount of exercise to stimulate muscle growth.

Do border collies grow quickly?

Border collies will experience a rapid growth spurt from around 3-10 months. Growth will, of course, continue after 10 months but at a much slower pace. During the period of rapid growth, it’s crucial to allow sufficient rest while avoiding over-exercising.

Thank you for reading! Back to more Border Collie articles >


Before making any decisions that could affect the health and/or safety of your dog, you should always consult a trained veterinarian in your local area. Even though this content may have been written/reviewed by a trained veterinarian, our advice to you is to always consult your own local veterinarian in person. Please read our full dislcaimer if you have any questions.