How to Tell Your Guinea Pig’s Age (3 Methods)

Perhaps you recently adopted a new guinea pig from a shelter or a previous owner and their age is unknown. Is there a surefire way to determine a guinea pig’s age? Guinea pigs are pretty good at concealing their age, but luckily, there are a few tips and tricks you can use to get a rough idea.

Size, weight, health, behavior, energy levels, and thickness of the nails can all be useful factors in determining a guinea pig’s age. While it can be difficult to pinpoint an exact age, it’s usually easy to determine between young, adolescent, adult, and senior guinea pigs.

Guinea pigs generally live between 4-8 years, so knowing your guinea pig’s approximate age helps to give you a timeline for how long you’ll have your new furry potato and how best to care for them as they approach their golden years.

Keep reading for 3 different ways you can determine your guinea pig’s age, as well as some ways to tell if your guinea pig is approaching their senior years.

Size and Weight

Size and weight can be helpful factors for determining a guinea pig’s age, particularly in guinea pigs under 1 year of age. This method is not always accurate on its own, as some breeds and individuals can vary in size. Peruvians, rex guinea pigs, or mixes of these breeds often grow larger than average guinea pigs.

Weight can also vary due to health and previous care. For example, adolescent guinea pigs can appear older if they were fed too many pellets in their previous home and put on weight too quickly. On the other hand, malnourished or underfed piggies can appear thinner and younger than they actually are.

Guinea pigs under a year old are easier to age based on size and weight, as adults over 12-18 months generally stay at a steady weight until their senior years.

Baby guinea pigs grow exponentially in their first 4 months of life and reach almost their adult length by 4-6 months of age. After 6 months of age, their growth slows significantly, but they will continue to put on weight slowly until they reach about 12-18 months old.

The following table shows the average weights of baby guinea pigs as they grow:

AgeAverage Weights
Birth60-120 grams
1 Month Old120-180 grams
2 Months180-240 grams
3 Months270-360 grams
4 Months360-480 grams
5 Months480-700 grams
6 Months600-900 grams
1 Year700-1100 grams

While guinea pigs finish the majority of their growth by 6 months old, they will not fill out completely until they are over a year old. If your guinea pig has a relatively lean body shape, there’s a good chance they are under a year old.

While some guinea pigs remain on the thin side for their entire lives, the vast majority of piggies chunk out a little as they get older. Guinea pigs between 1 and 3 years old are generally more filled out with good muscle tone and shiny, healthy fur.

I’m not fat, Mom; it’s called fluffy!

The average weight for full-grown adult guinea pigs is 900-1300 grams for males and 700-1100 grams for females. Guinea pigs closer to a year old are generally on the lower end of these ranges, while middle-aged piggies may creep up a little on the scale.

For example, here are the current weights and ages of some of my guinea pigs:

  • Rocket – Male – 6 Months – 898 grams
  • Clover – Female – 7 Months – 879 gram
  • Cheese – Male – 10 Months – 992 grams
  • Ciara – Female – 10 Months – 848 grams
  • Skittles – Female – 1.5 Years – 1018 grams
  • Skylar – Female – 2 Years – 1093 grams
  • Willow – Female – 3 Years – 1085 grams
  • Peach – Female – 4 Years – 1057 grams

As you can see, the weight gradually increases with age. Usually sometime between 1 and 2 years old, the numbers plateau and stay about the same until guinea pigs reach their senior years, where it may decrease again slightly.

Peach (my 4 year old) has actually already started to see a slight drop in weight from her prime years, as she used to sit in the 1100 gram range, being a slightly larger Peruvian mix.

Behavior and Energy Levels

Another way you can estimate a guinea pig’s age is by their behavior and activity levels.

Baby guinea pigs under 6 months old are much more active than any other age range. They will frequently popcorn, jump, and excitedly run laps around the room or cage.

Guinea pigs under 6 months also tend to be jumpier, sometimes more skittish, and less inclined to sit and cuddle on your lap. They have a short attention span and a stronger desire to run around and explore.

Babies are often more vocal and more nibbly than older guinea pigs too. Guinea pigs will chew and squeak throughout their entire lives, of course, but it’s not quite as excessive as when they are young.

Babies frequently nibble or gently bite your fingers or arms while you hold them, and they also love to chew or nibble things in their cages or on the floor. Guinea pigs take in a lot of information through taste and touch, which is why young piggies are so inclined to nibble things to learn more about their environment.

Baby Skittles is curious about the new food.

Between 6 months and 1 year old, guinea pigs should still be quite active, but their hyperactive baby stage starts to gradually slow down. They may zoom around less frequently, become less nibbly, and start to popcorn in less exaggerated ways (ie. head flicks, mini jumps where they don’t completely leave the ground.)

Between 1-4 years of age, guinea pigs usually stop running around just for the enjoyment of it. However, they should still be curious, active, and eager to explore their environment. Adult guinea pigs popcorn from time to time, but usually less often, and not the full body leaps into the air like the youngsters.

Adult guinea pigs are often more comfortable in their environment as well. You may notice them lounging around in the open while relaxing in their cage. They will often lounge outside their hidey houses and kick their feet out behind them to relax.

Skylar is happy and content with life.

Adults are also more likely to chill with you on the couch than young guinea pigs. As a general rule, guinea pigs seem to get calmer and more laidback with each year of age.

However, there are always exceptions to this rule. Some guinea pigs have chill personalities almost off the bat. On the other hand, active breeds like Abyssinians may never truly chill out. Some guinea pigs also have more skittish personalities and can take longer to reach a stage where they are calm and relaxed.

Nail Thickness

Nail thickness is one of the best ways to guess your guinea pig’s age. Guinea pig nails thicken gradually throughout your piggy’s life, so typically the thicker they are, the older your guinea pig is.

I’ll attach some pictures below of some of my guinea pigs’ nails and their ages.

Skittles at 4 Months Old

Rocket – 6 Months Old:

Cheese – 10 Months Old

Skylar at 1 Year Old

Willow at 2 Years Old

Daisy – 3 Years Old

TJ – 5 Years Old

A baby guinea pig’s nails start out very short, thin, and sharp. They can scratch you very easily at this stage of life. When clipping their nails, you’ll find that there is not much to clip at all except the tiny pointy tip.

Nails start to grow faster between 6 months and 1 year old, but they will remain pretty thin and relatively sharp. Between 6 months and 2 years old, you may want to clip more frequently to keep up with the faster nail growth.

As time passes, the nails become thicker, with duller tips. They become less pointy and don’t scratch you as easily anymore.

As your guinea pig reaches 3-4 years old, their nail growth typically starts to slow down. White nails get a bit yellowish and nails tend to get a little crooked and lie to the side a bit. However, if the nails weren’t maintained regularly at a young age, they can start to grow sideways at an earlier age.

Signs Your Guinea Pig is a Senior

As guinea pigs approach their senior years, there are usually several telltale signs. Starting at 4 years old, guinea pigs often lose a bit of weight and muscle mass. They may appear slightly bony, or you may be able to feel their spine or hips as you pet them.

Seniors are generally less active than adults and may even be starting to show early signs of stiffness or arthritis. They may stumble slightly on occasion or hesitate before jumping into a box or climbing a ramp. Some senior guinea pigs may even struggle to clean themselves thoroughly and can start to smell a little. If this occurs, they may need occasional baths and assistance cleaning.

Some seniors develop blindness or cataracts, making their eyes appear cloudy. This does not happen with all guinea pigs of course, but it can occur in some piggies as they age.

Besides this issue, guinea pig eyes should be bright and clear their entire lives and generally don’t change. Droopy or watery eyes are signs of a health condition and should be assessed by a veterinarian.

As guinea pigs continue to age, their nails often get thinner again and more brittle. They also grow at a much slower rate. Subtle fur changes can also occur in senior piggies. Their fur may get thinner and lighter in color. Dark patches may become mixed with lighter-colored hairs, similar to humans getting grey hair with age. Their fur may also become more ruffled looking, and not as sleek and shiny as it was in their prime.

Older guinea pigs generally sleep longer and more deeply than young or adult guinea pigs. They also may start taking “death naps” where they go into a deeper sleep and are harder to wake up. When they do this, they often lie almost on their side with their eyes partially open and don’t usually wake immediately when you look at them or make a noise.

It can be panic-inducing at times, but they generally wake up after a few seconds and look at you innocently and unknowingly. I’ve personally never seen guinea pigs take death naps before 4 years old, so it’s generally a senior thing.

Signs of aging can appear sooner in some guinea pigs, and be less apparent in others. Some guinea pigs lose muscle mass and even develop early arthritis right at 4 years old, but some retain most of their youthful appearance until 5 or 6.

Genetics and overall health can impact the way your guinea pig ages and make it difficult to tell sometimes. However, by watching closely for subtle signs, you can usually see the impact of aging in most guinea pigs.

As your guinea pig ages, it’s a good idea to keep a watchful eye on their health. Seniors in particular are more prone to health conditions. Dental issues are a common problem, as guinea pigs often lose muscle in their jaw as they get older, potentially causing the back molar teeth to grow out of alignment.

Weekly weighing is a good idea for all guinea pigs, but especially seniors, as weight loss is often the first sign of a health problem.


Knowing your guinea pig’s age helps you better care for them at their current stage of life. It also helps you know what to expect in terms of lifespan and behavior for the piggies in your care. The methods above can help you to estimate a guinea pig’s age, but individual factors like personality and genetics can impact how they show their age.

Regardless of how old your guinea pig is, a healthy diet and lifestyle is crucial to maximize their time with you. For more information on fresh foods that boost your guinea pig’s health, check out our Guinea Pig Food Chart for a complete list of fruits and vegetables and how often it’s safe to feed them to your furry potato.

Once you’ve narrowed down your guinea pig’s age, you may also be interested in knowing what your guinea pig’s age is in human years.

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