When Do Jack Russells Stop Growing?

By John Martin - February 15, 2022

Jack Russell puppy in grass

Jack Russell Terriers are generally small in size and loud and lively in temperament. They keep growing up to a certain point and manage to reach a certain size, beyond which their growth rate stabilizes.

Here, you can find out more about when Jack Russells stop growing along with the size that they reach and factors that can affect this kind of growth. Let’s begin!

At What Age Do Jack Russells Stop Growing?

Jack Russells tend to have a lifespan of 12-14 years, although this can also extend to 15-16 years in many cases. Does this mean that these dogs will keep growing for several years?

Just as the physical growth of human beings becomes standard and stable after a certain point, the same applies to dogs, including Jack Russells.

You can expect these dogs to grow until they are 12 months or a year old, following which their size and weight are likely to remain the same. There can be a few differences depending on your specific dog, although the general age tends to remain the same.

Growth Rate

Jack Russells usually have a rapid growth rate since they do most of their growing in the first year of their lives, although dog years generally work differently than human years do.

When your Jack Russell is still a newborn or a puppy, they tend to grow by around a couple of inches and pounds every month until they reach around 8-10 pounds of weight and less than 10 inches of height by the time they are four months old.

Beyond this, the growth rate quickens a bit, allowing them to grow by 2-3 pounds every month until they reach their ideal weight of around 15-18 pounds by the time they are 10-12 months old and a height of around 12 inches by this time as well.

Their growth rate beyond 12 months will then either slow down significantly or almost entirely stop.

Thus, to sum up, by the time they are 12 months or a year old, they will weigh around 13-18 pounds and measure around 10-15 inches in height, with an average height being around 12 inches.

Depending on the specific condition of your dog, however, they might reach this size either a couple of months earlier or later.

Factors Affecting Growth

Young Jack Russell

There are several factors that affect the growth of Jack Russells. Even though the breed is the same, the specific conditions that each dog is born into or can grow into will differ which can then determine their growth.

We will take you through some of these factors in this section.


What and how often your Jack Russell eats is an extremely important factor that can affect growth. Provided that you give your dogs a well-balanced and nutritious diet, they will be able to grow well at their usual growth rate and up to their standard size.

You should give them a diet with a balance of water, proteins, carbohydrates, healthy fats, minerals and vitamins so that they can grow and develop properly. Avoid too little or too much of a certain nutrient as this could be harmful to your Jack Russell.

You will also need to watch out for potential allergies and reactions.


Jack Russells are extremely active and agile dogs. They have high levels of energy and require daily physical exercise.

This could include long walks, runs, fetching, games and other activities. Provided that your Jack Russell receives a good amount of this kind of exercise, they will be able to grow well until they are a year old.

This kind of exercise can also strengthen their bones, muscles and mind while also regulating how much they weigh so that they do not end up becoming overweight.


Genetics can also be an important factor when it comes to determining how big your Jack Russell will grow and by when they will be able to reach their full size.

For instance, if the parents of your Jack Russell were on the larger side in terms of size (that is, around 15 inches and 18 pounds), then it is likely that your dog will grow up to that size as well. The same applies to smaller sizes.

However, in this case, you do not need to worry about extreme or unhealthy growth conditions unless there is a severe genetic condition.


It is likely that the sex of your Jack Russell will affect their growth as well as when they will stop growing. However, this is not a cause for concern since the difference will be quite small unless there is some other issue with your dog’s health and lifestyle.

In terms of sex, then, females are likely to achieve their maximum size and weight slightly earlier as compared to males, although their standard size is usually a couple or more inches and pounds lesser than that of males.

Males, then, are bound to be bulkier than females.

Health Concerns

Health issues related to your Jack Russell can also have an impact on their growth and when they will stop growing.

For instance, if they have growth impairments, stunting, muscular weaknesses and abnormalities, heart conditions, respiratory issues or others, then this might either directly or indirectly affect their growth, causing them to be smaller or larger than healthy levels.

Other conditions such as infections, worms or allergies can also affect their growth or stop their growth too soon.

If you find that your Jack Russell is exhibiting symptoms of any of these health issues, then you should take them to the vet immediately.


This is a minor factor but is still worth mentioning due to its impact on the growth of Jack Russells.

Generally, Jack Russells have a relatively longer lifespan that can extend up to 16 years in completely healthy conditions and lifestyles. In some cases, this can also range around 12-16 years depending on your dog.

In most cases, Jack Russells will grow until they are a year old. However, if their lifespan ends up reducing considerably, then their growth might get affected too, especially if they were born or are likely to die prematurely.

As long as they reach their size within a year, however, you will not need to worry too much about the size anymore.

Also Read: Are Jack Russells Good With Kids?

Keeping Your Jack Russell Healthy

You can maintain the overall health of your Jack Russell through the following ways so that they can grow well within the first year of their life.

Provide Stimulation

You should provide regular physical as well as mental stimulation to your Jack Russell so that they can remain healthy and happy while also being able to grow to their required extent and size.

Give them daily physical exercise so that they can release their energy and become calm while also strengthening their muscles. Physical exercise can also be a good way to improve their mood, whether through walks, runs or games.

Mental stimulation can also keep them occupied and vigilant so that they can work their brains and use their energy. This could include games, puzzles, small tasks or even simply playing with chew toys.

Provide Healthy Meals

It is extremely important to feed your dogs in a healthy manner so that they can absorb all the required nutrients and use them to keep growing well until they reach a proper size.

Provide them with their meals at regular intervals of the day while also being careful about the quantity and contents of the food. You should also buy their food from reliable and healthy brands.

Depending too much on a certain kind of food is also unwise since it could lead to poisoning and other health issues in your dog while also creating an imbalance in their weight.

Provide Care and Attention

Apart from healthy meals, you should also look after the fur, coat, skin, nails and teeth of your Jack Russell so that they remain clean and hygienic.

If these end up becoming too dirty, then they might fall sick through infections, allergies and bacteria.

You should also look after the emotional and mental health of your dogs so that they remain as happy or content as possible. Play around with them, give them affection, cuddle with them, give them open space and take them out frequently so that they remain happy.

Make sure you do not neglect them as this could lead to a host of issues.

Also Read: Best Brush for Jack Russells: Top Picks and Reviews

Prevent Diseases

It is important for you to do what it takes to prevent diseases. Apart from a healthy diet and lifestyle, you should also undertake regular checkups and keep track of symptoms of certain unavoidable diseases so that you can at least take them to the vet and start the treatment early on.

This can help your Jack Russell grow well and get better soon enough.

Final Thoughts

Jack Russells generally tend to stop growing by the time they are 12 months or one year old, with minor distinctions likely depending on several factors such as diet, exercise, sex, genetics, lifespan and health issues.