How to Tell the Age of a Rat: A Guide for New Owners

How to Tell the Age of a Rat
How to Tell the Age of a Rat

Let’s face it; it can be very hard to know the exact age of a pet rat based on little information known or kept about the rat birthing cycle. Unlike dogs and cats, which have better records to establish age, pet rats are not as widely a domesticated pet as cats and dogs, which leaves physical signs and traits being the only true ways to know a pet rat’s true age outside of purchases from breeders. Just how can you tell the age of a rat?

So, what guidelines are available to tell the age of a rat? To tell the age of a pet rat, examine the following characteristics:

  • Size. The larger the rat, the older rat is in their life cycle.
  • Teeth Color. Bright yellow or orange teeth is a sign of old age. 
  • Length of fur. Longer fur coats are an indication of advancing age. 

Since rats do not generally live longer than a few years, the aging process is much more advanced than what is seen in larger mammals. Due to the short life span of a pet rat, you have to look for certain signs that can alert you to the rat’s advancing age. This can be complicated; therefore, this guide will explore these concepts, as well as guide you through the stages of rat development over their lifespan. 


What Physical Signs Can Alert Me to a Rat’s Age?

Rats are around for only a short amount of time in human terms, and pet rats usually live for 2-3 years, 4-5 years in optimal health conditions. This is bittersweet to pet rat owners; therefore, it is only natural to wonder about the age of your pet rat, especially if the rat was already an adult rat the time of purchase. Since we humans view longevity through the years, a rat’s aging process will see physical signs at a very rapid rate. Let’s explore the physical signs to look for.


Rats begin their life cycle as very small babies, typically about 38.1 mm (1.5 inches). An adult rat can reach lengths upwards of 508 mm (20 inches), which is usually the length that can correspond to early-middle age for a pet rat. 

If you purchase an adult rat, you can easily gage that your new pet rat is fast-approaching the middle of their lifespan, if not at that point already. Young rats will be well under any length approaching 508 mm (20 inches). 

Note: A length of 508 mm (20 inches) is a calculation based upon the absolute maximum length of an adult rat from the tip of the tail to the nose. Adults can be much shorter than this estimate. 

Teeth Coloration

Another important sign to look for is the color of the rat’s teeth. All rats will have a yellow tint to their teeth, yet the lightness and darkness of this tint will increase with age. Young rats, which are any rats under the age of one year, will generally have teeth that are light yellow, therefore, if you purchase a pet rat and its teeth are not bright yellow, this is a good sign that you have a young rat. 

For rat’s over one year of age, the teeth will begin to take on a more rich yellow tent, and sometimes even turn slightly orange. If you have purchased a pet rat that has bright yellow or orange teeth, it is safe to assume that this rat is well in excess of one year. 

Length of Fur

Fur length is a bit tricky when trying to tell a rat’s age, yet this sign can still be used to get a rough estimate of age. If your pet rat has very thin and coarse fur, this can be a sign that the rat has not yet reached adulthood. Rats with long and thick fur coats are typically well over a year in age. Fur length is not particularly helpful for hairless rats, which is better suited by looking at teeth color and size to tell the age of this species. 

This is all useful in determining the age, but what exactly are the life stages of a pet rat? 

What Are the Stages of Development of a Pet Rat?

Here are some characteristics of pet rats once they reach a certain age:

  • Newborn-1 Week. Rats are very small at this stage and develop quickly from pink coloration to a very fine layer of fur.
  • 2 Weeks. Rats are more mobile and begin to open their eyes.
  • 3 Weeks. This is the stage when young rats reach all of the physical characteristics of a rat, just much smaller.
  • 1 Year. Rats at this stage are now considered adult rats, and the growth cycle slows considerably. 
  • 2 Years. Advanced teeth coloration may be present, as well as mobility issues.
  • 3 Years. Rats are considered to be advanced in age at this stage; body mass may deteriorate, and fur can grow longer.

This guide will help in making the best-educated guess in determining your pet rat’s age, although it can sometimes be difficult to guess a rat’s age once they are over a year in age. Since we tend to age living things in terms of years, how does a rat’s age correspond to this method?

Rat Years vs. Human Years

In terms of the human life cycle, a pet rat will live anywhere between 3-5 years. That is quite a lot of aging parameters in terms of human aging when you consider only a handful of years. Human beings are considered to be elderly roughly beginning in their 60s, which would be about two years of age in a rat. Advanced age is a guarantee of decreased performance and mobility; therefore, this is a good way to determine a pet rat’s overall age.

One day in the life of a rat is equal to 26.7 days in human years, which roughly correlates to 1 human day equaling a month of life in the rat lifespan. With this in mind, you can expect a deterioration of physical performance in your rat around the 2-year mark, which is essentially a sign of old age.  

Do Rats Act Differently As They Age?

With increased age also comes a lack of activity and overall interest than what was noticed months before. Since we only have biology and the particular traits of aging humans to relate rat age to, it is likely that your rat’s decreased performance could be a sign of advanced age. Older rats will still likely be active, just not as active as they once were. Lazy behavior may also be apparent in an older rat; not because they want to be, but because they are older. 

It is unfortunate, yet it is just a fact of a rat’s biological makeup. 


So, telling a rat’s age is not an easy process, yet there are some key things to look for to point you in the right guess:

  • Rats will slowly begin to decrease their activities once they reach old age.
  • Rats will display a darker shade of yellow or orange coloring of their teeth.

There are other factors to help tell a pet rat’s age, yet these two characteristics offer the most possible signs to confirm an older pet rat. If you buy an adult pet rat, realize that the rat’s lifespan will be much shorter than a baby rat.