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How Old is My Rat?

How old is my rat?

With special thanks to Katherine Milligan

We all know (and if you don’t, you should) that rats make some of the best small pets in the world. They’re sweet, social, playful, and INCREDIBLY intelligent. Oh, and they're super cute to boot. But when bringing these little fellas into your home, you probably want to know how old they are. I would. If you're adopting a rat that's less than three to four months old, they're not fully grown, so you can pretty much guesstimate their age within a few months. However, it's MUCH harder to tell if you're adopting a fully grown rat (between 250-400 grams). So, what should we look for as we try to pin down their birthday? We’ve got four physical characteristics that will help you determine how old is my rat?

Rat peeking out of a sleeve

As we’ve spoken about many times, generally, good health = good appearance and bad health = bad appearance. Pretty straightforward and very similar to humans. Conversely, looks can be deceiving in rats. Suppose you've adopted a rat previously living in a poor environment or eating a less-than-stellar diet. In that case, they could look much older than they actually are. If this is the case, priority number one is getting that rat healthy. Once they’re the picture of health, we can focus on guessing their age.


Your rattie’s size is a simple and easy way to determine how old is my rat, i.e., the larger the rat, the older they are. Unfortunately, rats have a short lifespan and age quickly. According to, baby rats are tiny and typically 1.5 inches/4 centimeters. Adult rats can grow as long as 20 inches/51 centimeters from nose to tail. 

Coat Check

Think of a rat’s coat as human skin. A baby, toddler, teenager (and many adults) has much prettier skin than I do. Generally, the younger the skin, the more untouched and flawless it is. The same goes for rats. The younger the rat, the silkier and smoother the coat. If a rat's coat has an average and even length, the rat is likely under 9 months. During puberty, the coat will develop thicker, longer guard hairs intertwined with the soft baby fur. However, male rats tend to have more coarse fur than their female friends, so keep this in mind. Suppose their fur is dull, missing, unkempt, and just looks all around kinda rough. In that case, the rat is likely a senior, possibly over 18 months.

Nevertheless, be warned that the dull coat may actually result from poor diet and health, and not necessarily age. Try top-quality food and fruits and veggies for some time. Then, if the coat bounces back, they're probably not as old as you'd initially thought.

Rat with a paw on their enclosure

Color of Their Teeth

While it's not a foolproof method, observing the rat's front incisors indicates a rat's age when wondering how old is my rat. Younger rat tooth coloration will be a pale yellow shade. As rats age, their tooth color will darken. In adult rats, the most common tooth color is dark yellow. As they transition to seniors, the tooth color will continue to darken and is commonly tinged with orange. Generally, the darker the tooth color, the older the rat.

Activity Level

Similar to other species, the younger the rat, the higher the activity level. We can all relate to slowing down as we age.

We're all ears graphic

The key indicators to determine how old my rat is are size, coat, tooth color, and activity level. Of course, you can always contact the person from whom you’d obtained the rat to try to get additional information, which I highly recommend anyway. As always, when bringing home a new rattie pal, they should have a thorough wellness exam from your trusted exotic vet. The vet will be able to give you an expert age guestimate. 

Whether you've adopted a young rat or an old one, they're gonna love you the same. So, while knowing their age is excellent, what's most important is your rat's happiness. And don’t forget to celebrate their Gotcha Day! I bet they’ll value the day they found their forever home the most.

DISCLAIMER: The links and information are being provided as a convenience and for informational purposes only; they do not constitute an endorsement or an approval by Small Pet Select of any of the products, services or opinions of the corporation or organization or individual.

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