Border Collie Puppy Growth: A Complete Month-by-Month Guide

Understanding Border Collie puppy growth is essential for any owner preparing to welcome the world’s smartest dog breed into their family. While these puppies are famously intelligent, their development is a unique mix of rapid physical growth and a much slower burn toward mental maturity. Bringing a Border Collie puppy into your home is less like getting a pet and more like adopting a high-velocity lifestyle.

A common mistake new owners make is assuming that once their puppy looks like an adult, they will act like one. In reality, the Border Collie is a breed of contrasts. Physically, they may reach their near-adult height by 10 or 12 months, but mentally, they often remain “puppy-like”—retaining that boundless, kinetic energy—well into their second or third year. This disconnect can be challenging if you aren’t prepared for the “teenage phase,” where their body is capable of high-performance athletics, but their brain is still testing every boundary you set.

In this Border Collie puppy growth guide, we will break down your puppy’s journey month by month. We’ll cover the physical milestones, such as when their ears might finally stand up (or flop over!), to the critical behavioral phases that define the breed. Whether you are looking for a working partner or an active family companion, knowing what to expect will help you survive the chaos and enjoy the brilliance of raising a Border Collie.

Note: Every dog is an individual. This guide provides averages based on typical breed standards, but always consult with your veterinarian or a reputable breeder regarding your specific puppy’s health and development.

Quick Reference: Border Collie Puppy Growth Chart (Estimates)

While every dog is an individual, looking at the average growth curve can help you track if your puppy is developing on schedule. Border Collies are medium-sized dogs, but their growth spurts can be dramatic. You will likely notice they get “tall” before they get “wide,” often leading to a lanky, awkward teenage phase before they fill out their famous double coats.

According to the American Kennel Club (AKC) breed standard, adult Border Collies typically stand between 18 and 22 inches at the shoulder. However, weight can vary significantly depending on the dog’s lineage (more on that below).

Important Note on Lineage: There is often a size difference between Show Lines (bred for conformation) and Working Lines (bred for herding sheep). Working Border Collies are often leaner, lighter, and more athletic in build, while Show lines tend to be stockier with heavier coats. If your puppy seems smaller than the average but is active and healthy, they may simply come from a working pedigree.

For a deeper dive into breed standards and health, the Border Collie Society of America offers excellent resources for new owners.

The “Sponge” Phase: 2 to 3 Months (8–12 Weeks)

When you first bring your Border Collie puppy home, usually around 8 weeks old, you are entering the most critical learning period of their life. We call this the “Sponge Phase” because their brains are rapidly forming new neural connections. What they experience—and do not experience—during these weeks will shape their temperament for life.

Physical Changes: The “Wonky Ear” Stage

Physically, this is the peak “fluff ball” stage. You will notice rapid weight gain, often adding 1 to 2 pounds per week. One of the most endearing (and hilarious) traits of Border Collie growth happens now: the ears. Border Collie ears can be prick (standing up), semi-prick (tips folded), or drop (floppy). Between 8 and 12 weeks, the cartilage is hardening, and you may see one ear stand up while the other flops, or both ears changing positions daily.

Behavioral Expectations: The Herding Instinct Awakens

You might notice that your cute puppy has a habit of biting your ankles or chasing children who are running. It is vital to understand that this is not aggression; it is instinct. Border Collies have been bred for centuries to control the movement of sheep by nipping and staring. Without sheep, they will try to herd you, your kids, or your vacuum cleaner.

Training Focus: Socialization and Confidence

While potty training and crate training are immediate needs, your primary focus must be socialization.

According to the American Veterinary Society of Animal Behavior (AVSAB), the primary window for socialization closes around 14 weeks. This doesn’t just mean playing with other dogs; it means exposing your Border Collie to:

• Different surfaces: Grass, gravel, tile, slippery floors.

• Noises: Traffic, vacuums, thunderstorms (played softly on a speaker).

• People: Men with beards, people wearing hats, children, and seniors.

Border Collies can be sensitive and prone to noise phobias if not properly desensitized early. Positive exposure now prevents a fearful, reactive dog later.

Care Tip: Start touching their paws and looking inside their ears immediately. You will need to trim their nails and groom them for the rest of their lives; making this a positive experience with treats now will save you a headache later.

The “Land Shark” Phase: 3 to 4 Months

If you thought the first few weeks were tiring, welcome to the “Land Shark” phase. This is notorious among Border Collie owners as one of the most testing periods. Your puppy is growing rapidly, their confidence is surging, and their mouth seems to be their primary tool for interacting with the world.

Physical Changes: The Teething Torment

Around 12 to 16 weeks, your puppy will start losing their needle-sharp deciduous teeth (baby teeth) to make room for their adult set. You might find tiny teeth on the floor, or you might just notice blood on a chew toy—this is normal.

Physically, the “cute fluff ball” look is fading. Their legs are growing faster than their bodies, giving them a lanky, colt-like appearance. You might notice them becoming slightly clumsy as they adjust to their new height.

Behavioral Expectations: Nipping and Chewing

The combination of teething discomfort and the Border Collie’s natural desire to control movement can lead to excessive nipping. They aren’t trying to hurt you; they are communicating and relieving gum pain. However, those sharp teeth hurt!

This is also when their energy levels spike. A 10-minute walk is no longer enough. If a Border Collie doesn’t have a job to do during this phase, they will invent one—usually involving un-stuffing your couch or “herding” the family cat.

Training Focus: Bite Inhibition and Brain Games

• Bite Inhibition: You cannot stop a puppy from biting overnight, but you can teach them to have a “soft mouth.” The Whole Dog Journal explains that teaching bite inhibition (learning to control the force of the bite) is actually more important than stopping the biting immediately. If they bite too hard, stop play immediately to show that teeth on skin equals “game over.”

• Mental Stimulation: You cannot tire out a Border Collie with physical exercise alone—you will just build a super-athlete who never sleeps. You must tire out their brain. Use puzzle toys, snuffle mats, or hide-and-seek games with kibble.

• Recall Foundation: Now is the best time to reinforce the “Come” command. They still have a “follow instinct” and aren’t independent yet. Use this to your advantage before adolescence hits.

Health Note: Since teething is painful, provide appropriate relief. Freezing a wet washcloth or using rubber chew toys can soothe sore gums. Avoid very hard bones that could fracture their fragile new teeth. For more on safe chewing options, VCA Hospitals offers detailed advice on dental development.

For in-depth brain training for your puppy, enroll in the Brain Training For Dogs course which develops your dog’s “Hidden intelligence” to eliminate bad behavior and create the obedient, well-behaved pet of your dreams. Sign Up Here.

The “Awkward Teenager” Phase: 4 to 6 Months

Welcome to adolescence. Between 4 and 6 months, your Border Collie will undergo significant changes that can be visually amusing but behaviorally frustrating. This is the stage where many owners feel like their well-trained puppy has suddenly “forgotten” everything. Don’t worry—it’s temporary.

Physical Changes: The “Puppy Uglies”

If your puppy suddenly looks patchy, scruffy, or like they are having a bad hair day, they have likely hit the “Puppy Uglies.” This is when the soft, fluffy puppy coat sheds to make way for the sleek, water-resistant adult double coat. The adult coat often starts as a strip of coarser hair down the spine, while the rest remains fluffy, creating a mismatched look.

Crucially, your puppy’s growth plates (the soft areas at the ends of the long bones) are still open and vulnerable. While Border Collies are famous for catching frisbees, you must limit high-impact jumping during this phase. According to the American Kennel Club’s guide on puppy exercise, repetitive jumping or sharp turns before full maturity can cause long-term joint damage.

Behavioral Expectations: The Second Fear Period

Just when your puppy seems confident, they may suddenly become terrified of a trash can, a hat, or a statue they’ve walked past a hundred times. This is known as a “fear period.” AKC experts explain that this is a normal developmental stage where the brain is reorganizing.

• Do not force them to approach the scary object.

• Do not coddle them excessively.

• Do: Let them observe from a safe distance and reward them for looking at it calmly.

Training Focus: The “Off-Switch”

Border Collies are not born knowing how to relax; they must be taught. If you constantly throw the ball every time they drop it at your feet, you are training them to be demanding.

• Teach “Settle” or “Place”: This command tells the dog to go to a specific mat or bed and stay there until released. It is the most valuable tool for managing a high-energy dog indoors.

• Selective Hearing: Adolescence brings independence. If you call your dog and they ignore you to sniff a bush, do not just keep calling. Go get them (calmly) or use a long line (leash) to prevent them from ignoring you. Consistency is key.

For a deeper dive into surviving this rebellious phase, check out the AKC’s guide to adolescent puppy changes, which covers both the behavioral and hormonal shifts occurring now.

Young Adulthood: 6 to 12 Months

By the six-month mark, your Border Collie will look less like a puppy and more like a small adult. However, do not be fooled by their appearance. This phase, often called the “Energizer Bunny” stage, is characterized by peak stamina and significant hormonal changes.

Physical Changes: Sexual Maturity and “Filling Out”

Between 6 and 9 months, your puppy will reach sexual maturity.

• Females: Most female Border Collies will experience their first heat cycle during this window. You may notice swelling and behavioral changes (clinginess or irritability).

• Males: Male dogs may start lifting their legs to mark territory and may become more interested in the scents of other dogs.

While height growth slows down significantly, your dog will continue to “fill out,” building muscle mass and chest width. This is also a critical time for discussing spay/neuter timing with your vet. Recent research suggests that for active breeds, waiting until growth plates close (often past 12 months) may reduce orthopedic risks. The American Animal Hospital Association (AAHA) provides guidelines on how to make this decision based on your dog’s specific lifestyle and health.

Behavioral Expectations: The Need for a Job

If you haven’t given your Border Collie a “job” yet, they will likely resign from being a good pet and apply for the position of “Household Menace.” Their herding genetics demand a task. This doesn’t mean you need sheep; it means they need to feel useful. Without directed activity, obsessive behaviors (shadow chasing, tail spinning, or staring at lights) can develop.

Training Focus: Advanced Skills & Agility Foundations

Now that their attention span is improving, you can move beyond “sit” and “stay.”

• Impulse Control: This is the antidote to their high energy. Teach “Leave It” and “Wait” at doorways.

• Agility Foundations: You can introduce your dog to the sport Border Collies are famous for, but keep it “wheels on the ground.” You can practice tunnels, weave poles (slowly), and handling maneuvers. Do NOT start high jumps yet. The AKC Agility Getting Started Guide emphasizes that foundation training is about communication and confidence, not just speed and jumping.

Pro Tip: This is the age where many Border Collies end up in shelters because owners cannot handle the energy. Consistency, crate training (for enforced naps), and mental stimulation are your best tools for survival.

Full Maturity: 12 to 24 Months

Congratulations! You have survived the first year. By 12 months, your Border Collie is technically an adult, but seasoned owners often smile at this milestone because they know the truth: a Border Collie is often not really mature until age two or three.

Physical Maturity: The Final Form

By their first birthday, most Border Collies have reached their full height. However, they will likely continue to gain weight and muscle mass until they are 18 to 24 months old.

• The Coat: If you have a rough-coated Border Collie, this is when the magnificent “mane” and heavy tail feathering fully come in.

• The Build: The chest will broaden, and they will lose that last bit of lanky adolescent look.

Mental Maturity: Focus Meets Energy

While the frantic puppy energy might taper off slightly, it is replaced by serious endurance. The difference now is focus. A one-year-old Border Collie has a longer attention span and can handle more complex training chains. However, they are still prone to “testing” you. If you slack on consistency, they will happily revert to their own rules.

Transitioning to Adulthood

This period involves two major transitions:

1. Dietary Switch: It is time to switch from high-calorie puppy food to a high-quality adult formula. Border Collies have high metabolisms, so active dogs may need performance blends, but be careful—if they aren’t working sheep daily, they can get overweight easily. The American Kennel Club (AKC) provides guidelines on how to make this transition gradually to avoid stomach upset.

2. Sports Clearance: This is the green light many owners have been waiting for. Once your vet confirms that growth plates are closed (usually via X-ray), your dog is cleared for high-impact activities. You can now introduce full-height jumps in agility, flyball, or intense frisbee sessions.

Behavioral Note: You might notice your dog becoming more protective or alert. The “watchdog” bark may develop more fully now. It is important to acknowledge their alert but teach them that “that’s enough” so they don’t become nuisance barkers.

Factors That Affect Growth

While the charts and timelines give you an average, your Border Collie is an individual. Several key variables will determine exactly how big they get and how quickly they mature.

1. Genetics: Show Lines vs. Working Lines

The biggest factor in a Border Collie’s size and build is their lineage.

• Show Lines (Conformation): Bred to meet a specific physical standard for the show ring, these dogs tend to be stockier, with heavier bone structure and much thicker “rough” coats. They often weigh more, even if they aren’t taller.

• Working Lines (Herding): Bred strictly for function, these dogs vary wildly. They are often leaner, lighter, and more athletic to facilitate speed. A working-line female might only weigh 30 lbs and be perfectly healthy.

• The “Sports Mix”: Many breeders now mix lines to create the ultimate agility dog—often resulting in a “medium” build.

2. Nutrition

Border Collies are high-energy engines that require high-quality fuel. However, “growing” doesn’t mean “overfeeding.”

• Puppy Food: Large-breed puppy formulas are generally not necessary for Border Collies (who are medium breeds), but a formula with controlled calcium/phosphorus ratios is still important for bone health.

• Body Condition Score: Instead of obsessing over the scale, learn to assess your dog’s body condition. You should be able to feel their ribs (but not see them) and see a defined waist tuck. The World Small Animal Veterinary Association (WSAVA) provides a global standard for assessing body condition that every owner should learn.

3. Spay/Neuter Timing

When you choose to alter your dog can physically change how they grow. Sex hormones play a role in the Border Collie puppy growth and telling the growth plates when to close.

• Early Neutering: If a dog is neutered before puberty (before 6-9 months), the growth plates may stay open longer. This often results in a dog that is taller and leggier than they would have been otherwise.

• Orthopedic Risks: Some studies suggest that delaying sterilization until physical maturity (12+ months) may reduce the risk of certain joint disorders, particularly in active breeds.

• Consult Your Vet: This is a medical decision. The American Veterinary Medical Association (AVMA) recommends discussing the specific risks and benefits for your dog’s breed and lifestyle with your veterinarian.

Border Collie Puppy Growth Conclusion

Raising a Border Collie is a marathon, not a sprint. The journey from a 10-pound ball of fluff to a high-speed, intelligent working partner is filled with challenges that test your patience—and your vacuum cleaner.

While the physical growth chart tells you about pounds and inches, the real growth happens in the bond you build. A Border Collie does not just want a master; they want a teammate. The hours you spend navigating the “Land Shark” phase and the “Rebellious Teens” will pay off when you have a dog that can read your body language and anticipate your next move.

Remember, if you are feeling overwhelmed about your Border Collie puppy growth, you are not alone. The vast majority of Border Collie owners have stood exactly where you are, wondering if their dog will ever stop moving. They will (eventually). Until then, keep training, keep playing, and enjoy the ride.

Frequently Asked Questions (FAQ)