How To Know How Old A Guinea Pig Is (5 Simple Tips)

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Knowing the actual age of your guinea pigs will help make informed decisions about their health. You’re gonna struggle to figure out how old your guinea pig is. So, how can you tell how old your guinea pig is?

You can tell how old your guinea pig is by looking at their nails, eyes, teeth, behavior, and size. These will all change as your guinea pig gets older. So you can tell if they are a baby, an adolescent, or an adult. These factors won’t reveal your guinea pig’s exact age, but they can give you a rough estimate.

a guinea pig saying that he won't tell how old he is

So yes, it’s possible to know how old your guinea pig is, even without knowing their exact birthday! By examining a few aspects, you can get a pretty good idea of how old they are. Let’s dig deeper below to learn more about how to tell how old a guinea pig is.

1. Nails

One of the best ways to tell how old your guinea pig is is by looking at their nails. A guinea pig’s nails will go through different stages as they age.

For example, a young guinea pig’s nails will be pointy and translucent (or partially see-through) with a whitish color. That’s because they’re still growing and haven’t reached their full length yet.

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But once they turn a year old, their nails will become thicker and more rounded. The translucent color will start to change into an opaque yellow.

The science behind that is that the keratin in their nails starts to harden and change color as they age (pretty cool, right?)

Then, as they get into their sunset days, the thick and yellow nails will begin to curve in and become blunt and crooked. When you notice these signs, chances are that your little friend is at least 3 to 4 years old.

2. Eyes

Eyes aren’t for providing a glimpse into your guinea pig’s health. Looking at your guinea pig’s eyes can give insights into how old they are – unless you have a sick pet.

For example, young guinea pigs below a year old will have large, black, shiny eyes. This is a sign of good health and youth.

But, their eyes will become smaller (relative to their body size) and less shiny as they age. In fact, in some cases, the black color may even start to fade and turn into a duller shade.

Plus, you may notice that your guinea pig’s eyes may become “sunken in” as they age. This is true if they’re not getting enough exercise or their diet isn’t well-rounded.

All in all, by looking at your guinea pig’s eyes, you should be able to get a pretty good idea of how old they are.

“Young guinea pigs have large, black, and shiny eyes. But, as they age, their eyes will become smaller and less shiny.”

3. Teeth

Guinea pigs’ teeth are much like human nails in that they are ever-growing. We call that elodont dentition, which is different from humans. You see, our teeth only grow to a specific size and then stop.

But far from that, it’s still possible to look at your pig’s teeth and predict their age. You see, guinea pigs’ teeth start growing days after they are born. Much like infants, the teeth remain small and thin during at first. They’ll also stay white throughout their first year.

But, as days go by, the teeth will grow larger and yellow. Sometimes the teeth may also develop ridges and even begin to break. When you notice any of these signs, know that you aren’t dealing with a baby guinea pig no matter what the seller says.

“Guinea pigs’ teeth grow throughout their lives. But they’ll grow white and thin in the first year. After that, they’ll start to yellow, develop ridges, and break in bits.”

4. Behavior

Behavior won’t only tell you the personality of your guinea pig. By looking at how your pig behaves, you can also tell how old they are.

They are also more comfortable with being held and touched. In fact, they may even enjoy a good back scratch from time to time!

For example, young guinea pigs tend to be more active and playful. They’ll also be more curious and ready to explore.

Baby guinea pig: Hey, what’s this long, shiny, silver thing? Oh, look there’s a ball inside it. When I press on it, all this water pours out! Too cool.


After all, they don’t know much about the world yet, so everything is new to them.

Older guinea pigs will be more subdued and less active. They’ll also be less curious and exploratory. They’ve seen it all before and aren’t as excited by new things.

Be suspicious of any sudden change in your pig’s behavior. For instance, be careful if you notice normally active guinea pigs becoming suddenly subdued.

In these cases, it doesn’t mean they’re getting old. It could be a sign of illness. At any rate, it’s always best to get your fur baby checked out by a vet. You just need to make sure that they’re okay and not sick.

5. Size

While it may not be the most accurate way to tell a guinea pig’s age, their size can can give you clues about how old they are. Guinea pigs are born small and they need some time to grow before they are their full size.

By the time a guinea pig turns 3 months old, they should weigh about 18 ounces in their healthy state. But, as they approach the one-year mark, their weight should range between 24 and 42 ounces.

Speaking of their size, guinea pigs measure 3 to 4 inches long at birth. Assuming they grow at a healthy rate, they should reach 6 to 8 inches by the time they are 2 months old. As they are more than 4 months, that length will increase to about 8 to 12 inches.

Birth3 – 4 Inches
8 weeks6 – 8 Inches
16 weeks8 – 10 Inches
14 months>8 Inches

Like I said before, looking at the size of your guinea pig isn’t the best way to tell the age of your little friend. Malnutrition may cause your little friends to weigh much less than they should.

But if your pig is of a healthy weight, then you can use their size as a general guide to estimating their age.

Now, if a guinea pig doesn’t get the right food when it’s young, it’ll often make up for some of the lost nutrients as it gets older – and keep growing.

That is, if the poor thing ends up in a good home and is well-cared for. In cases like this, the piggie will keep growing past 6 months up until 2 years of age.

“Guinea pigs that are more than a year old will weigh at least 24 ounces. They should also measure at least 8 inches in length as long as they are healthy.”

So, there you have it. You can either use these age-telling tips individually or together. (Personally, I recommend using a combination of them).

But, remember that only give you a general idea of your guinea pig’s age and not an exact number.

The only way to know how old your little friend is FOR SURE, is if you adopted from a breeder or you were there to witness the birth yourself.

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When Does A Guinea Pig Become An Adult? 

A guinea pig becomes an adult from 6 months to about 5 years. When your pig reaches 6 months old, they’ll have grown into their adult size and weight.

But this doesn’t mean that your guinea pig won’t become sexually mature till then. Boars are sexually mature at 3 months old (but can conceive at thre weeks old)  while sows can conceive as early as 2 months old. So if you don’t want your guinea pigs to get pregnant, be sure to separate them before they reach these ages.

Guinea pigs above five years old are seniors. Unlike their youthful counterparts, these guinea pigs need more care and attention. That’s because they are more susceptible to health problems.

How Old Are Guinea Pigs In Pet Stores?

a tip about baby guinea pig
Guinea pigs at pet stores are usually so young that they haven’t had any role models. Sometimes it’s best to pair up a young piggie with an older piggie, so that they can show them the ropes.

Guinea pigs at pet stores will vary in age depending on their availability. But these pigs will be anywhere between eight to twelve weeks old in most cases – still babies in guinea pig years. Even so, always ask the staff about the age of the guinea pig before buying.

Guinea pigs that are too young may not have received the proper care and socialization. As a result, they may be more prone to health problems and harder to handle.

Meanwhile, too old pigs may already have developed some health problems. So while they may be easier to handle, they may come with some underlying health issues.

How Big Will My Guinea Pig Get? 

Guinea pigs will grow to about 8 to 12 inches and weigh between 1.5 to 2.6 ounces. Even so, their full-grown size will depend on the breed and whether they are male or female.

For instance, guinea pigs like the American, Peruvian, and Teddy will grow to be on the larger side. But, breeds like the Abyssinian, Silkie, and Sheltie will be smaller in size.

As for the gender, males are usually larger than females. So if you’re looking for an enormous guinea pig, then you’re better off getting a male.

Why Is It Important To Know How Old Your Guinea Pig Is? 

Knowing the age of your guinea pig will allow you to make essential decisions on their care. For instance, you’ll know when to start feeding them solid food. You’ll also get to understand when to introduce them to other guinea pigs.

Besides, knowing the age of your guinea pig will help you;

  • Know how big they’ll grow
  • Decide space need
  • Choose the right type of food
  • Help them socialize
  • Determine their life expectancy

Final Verdict

The essence of knowing your guinea pig’s age goes beyond the mere need to organize a birthday party for them. It helps you understand how to better care for your pet and make decisions about their health.

And yes, by using the tips and tricks mentioned above, you should be able to get a pretty good idea of your guinea pig’s age.

But again, remember that these are only guidelines to give you a rough estimate of age and not exact numbers. If you need to know how old your guinea pig is, you should ask your vet. The vet will do a medical examination and give you an estimate of your guinea pig’s age.

Wanna Give Your Piggies
the 5 STAR Treatment?

Stop getting dirty looks from your piggies, because you forgot to do something for them...AGAIN. These colorful, chore charts will help you keep track of when to feed your fuzz butts, clean their cages, and much more. 


Exotic Animal Rescue and Pet Sanctuary. (n.d.). Guinea Pigs. EARPS. 

Hess L., Axelson R. (n.d.). Owning Guinea Pigs. VCA Animal Hospitals. 

Legendre FJ. Oral disorders of exotic rodents. National Library of Medicine. 2003 Sep; 6(3): 601–628. 

Pet Cosset. (2020, November 15). How To Tell A Guinea Pig’s Age? 3 Awesome Ways To Know! 

Quesenberry K., Donnely T. (2020, October). Breeding and Reproduction of Guinea Pigs. MSD Veterinary Manual. 

San Diego Zoo Wildlife Alliance. (n.d.). Guinea Pig.   

Woodgreen. (n.d.). Your guinea pigs’ health: what to look out for.

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