How To Tell How Old A Rat Is (With Examples)

Thinking about buying a rat but wondering how old your would-be rat is? Well, it’s very easy to tell how old young rats are with a bit of practice and we can show you everything you need to know about how to tell how old they are.

Our guide on how to tell how old a rat is (with examples) includes newborns, 1 day old, 2 day old, 7 day old, 14 day old, 18 day old, 25 day old, 28 day old,35 day old and 42 day old rats as well as how to tell the rough age of adult rats using their teeth and coat (and a simple check which has nothing to do with looking at rats at all).

The Rat Lifecycle

Rats are not the longest lived of animals. Pet rats will live for approximately 2-3 years and the most common cause of death, believe it or not, is tumors.

Their short lifespan means that they reach maturity fairly quickly and you can expect to find that a baby rat is ready to be separated from its mother at around 5-6 weeks old. Rats begin to wean even earlier than this.

They reach sexual maturity at around the 3 month mark and by about 6 months old they are considered to be fully grown.

This also means that a female rat can have up to 12 litters in a lifetime with around 8-12 babies in each litter. When they say, “breeding like rats”, they’re not far wrong, it’s possible for a female rat to have 150 or more babies in her life!

How To Tell How Old A Baby Rat Is

Please don’t buy baby rats. Newborn rats should never be separated from their mothers and we would recommend that you wait until rats are at least 5-6 weeks old before taking them into your home.

Fortunately, most reputable breeders won’t sell a baby rat that’s much younger than this and none should sell you a rat younger than 4 weeks old (the age at which rats wean) as it won’t survive away from its mother before this.

So, if you need to use this guide, it ought to be because one of your rats has given birth or you’re worried that a less reputable dealer is trying to sell you a rat that is too young.


The easiest place to begin is when baby rats look the least like rats. Newborn rats are almost like another creature completely – firstly, they are bright pink and completely hairless. They could almost be any rodent at all at this stage.

Each rat will weigh roughly 6-8 grams that’s not very heavy at all – in comparison a 25-cent piece (a quarter) weighs about 6 grams, so, if you have one in your pocket, you will be able to tell how much your rat’s babies are likely to weigh.

They can neither see nor hear as their eyes and their auditory canals are, for the moment at least, sealed.

If you can see a white spot in their stomachs – don’t worry this means they’re feeding, it’s their mother’s milk showing through their skins!

In fact, the time to worry is if you don’t see this because it may mean that the rat’s mother is not producing milk, or she is refusing to feed them. It’s unusual for a rat mother to refuse a child and it can be an indication that she has other problems due to the birth.

Please don’t handle the newborn babies, yourself. It is likely to stress out the mom who is probably, due to having given birth, a bit frazzled emotionally anyway. You may also damage the little ones at this stage – it’s best to give them a little time to get used to the world before you pick them up.

1 Day Old Baby Rats

Some of the most dramatic changes in your rats will take place in the first week of their lives and that’s because they’re developing rapidly. Unlike human babies, rat babies won’t get to be children forever and a day and within a few weeks they need to be fending for themselves.

In fact, they’ll be weaning before you know it.

On the first day, you’re going to notice that your rats start to change color. The bright pink of the day before is disappearing and their skin if already greying. This is good news; it means your rats are healthy and are getting fed enough for their bodies to start developing the way that they should do.

You may, if your mother rat leaves the cage for exercise, just gently handle the babies now but for no more than a few seconds and you should not damage the nest at all. You can clean around the cage (but don’t use any harsh smelling chemicals) but don’t touch the nest or the area just around it for now.

2 Day Old Baby Rats

You will see your rats getting darker over the next few days from day 2 until about day 7, they’ll get a few shades darker every day and that’s exactly what you want to happen. With a bit of practice, you can gauge roughly how old a rat is by how dark it is during this week but it’s not an exact science.

5 Days Old

The other thing that you’re likely to spot on day 2 is that the rats have become noticeably bigger than when they were born. The growth curve from baby to adult rat is quite linear and you should again, expect to see noticeable growth on a daily basis for a few weeks.

Assuming that these two things are OK, then you can be sure that your rats are getting on as expected.

7 Day Old Baby Rats

By day seven we’ve found that your rats will have a layer of fine fuzz that will, over time, develop into a lovely coat of hair. The rats no longer look newborn, but their eyes are still closed, and their ears are still sealed at this stage.

That means you still need to be very careful about managing their environment and taking of their mother because without her they’d still be helpless. You can gently pet baby rats of this age but again it shouldn’t be for much more than a few seconds. You don’t want to upset their relationship with their mother.

14 Day Old Baby Rats

You should find that their eyes and ears open up around day 14 and by now their fuzz is starting to look like rat fur. You can start to get a good idea of how your baby rats will look when they’re all grown up by this stage too.

As their sight and hearing has emerged, they’re going to start becoming curious and moving away from their mother more and more and exploring their environment. It’s important to just have a quick check over the cage and ensure that any possible hazards have been removed.

Watch out for strips of cloth, the floor of the cage should be covered if there are bars in the floor, etc. as you don’t want them to sprain or break a limb.

18 Day Old Baby Rats

Candy Rats – Rattery

By 18 days the rats are starting to look more like mature animals, and you can see them happily grooming themselves and each other. This is a nice phase in their lives when rats are often at their most playful and entertaining.

They’ve also started to diversify what they eat and you should find that they’re enjoying a wide range of foods but they won’t have weaned, yet, so please don’t think about separating them from their mothers, they still need her milk in order to thrive.

25 Day Old Baby Rats

Your rats should, by now, have developed most of their motor skills and control. You will notice that they race around the cage faster and are, perhaps, a little more boisterous than they once were, and they should be happy to play with you for a few minutes to an hour without any distress at all.

However, you should still be careful when you handle them as young rats are still very delicate.

28 Day Old Baby Rats

It’s weaning time or thereabouts by a month old, the rats ought to be breaking the habit of suckling on their mothers. It’s a happy time for mom who is going to be much less exhausted with her life when she no longer has to dedicate her time to feeding her babies.

It also doesn’t appear to be a problem for the young rats which seem to effortlessly switch over to other food without crying or becoming stressed. That makes weaning rats a much easier proposition than weaning human children.

35 Day Old Baby Rats

At this stage, you should find that they are still getting bigger and are noticeably heading towards their final size and shape. You may find that you can distinguish their secondary sexual characteristics at this point and if you can, you should separate out the males and females.

While rats of this age cannot, generally speaking, become pregnant – they will start to mount each other and it’s probably best to discourage incest in your rats and to avoid the female rats becoming distressed by the male ones.

42 Day Old Baby Rats

This is the last time to separate your rats. Going forward, if you put boys and girls together, you’re going to end up with more rat babies and as we’ve already seen, the rat lifecycle allows for a whole lot of pregnancies.

You rats are weaned and ready to fly the nest (or at least, leave the cage) and go to new homes where they will be as loved and cared for as you’ve loved and cared for them. Nice work.

How To Tell How Old A Mature Rat Is

OK, once your babies have grown up, it might be much harder to tell how old they are. Pet rats can live for up to 3 years, but they tend to look very similar for much of this time. This is one of the reasons it’s not recommended that you buy an adult rat but instead look for a young rat of about 6 weeks.

Not only is it harder to socialize an adult rat but they may not live very long which can be heartbreaking, particularly, it it’s your first pet rat.

However, if you do need to be able to tell how old an older rat is – there are 3 ways to go about it. 2 of them allow you to make a guess by looking at the rat, the third strategy is the best way to but, sadly, it’s not always viable either.

The Color Of The Rat’s Teeth

When a rat’s teeth come through, they tend to be an attractive shade of yellow. Over time, however, they get a bit darker and as a rat grows old – the teeth can change to an orange color in the rats’ final months.

Unfortunately, you cannot use a rat’s teeth to provide an accurate age for a rat. There is significant variation between individuals and it’s possible that you’ve found a rat with naturally orange-y teeth rather than a pensionable rat with a bit of orange color in their mouth.

This is important because it means that we can use teeth as something of a guideline and certainly, we’d recommend that you think twice before adopting a rat with orange colored teeth because of the potential for it to be reaching the end of its lifespan but not as a hard and fast rule.

It is also possible for the rat’s diet and general health to influence the coloration of its teeth and even a young rat, under the right/wrong circumstances can end up with an orange smile.

The Quality Of The Rat’s Coat

Rat’s are generally quite fastidious animals and they like to be clean and well-groomed and that means you can often get an indication as to how old a rat is from the state of its coat.

If it has a smooth, silky coat which looks lustrous and fine and is mostly even in length – the rat is probably under 6 months old (or maybe 9 months for females).

As rats mature they go through the equivalent of human puberty and their hair becomes coarser and less silky and this happens more dramatically in boy rats than girl ones.

Old rats, that is those over 18 months, on the other hand, may have rough hair, and missing lumps from their coat.

Again, this isn’t a hard and fast rule but if the rat has orange teeth and its coat is in something of a state, you can assume that rat is among the older members of its breed.

Asking The Rat’s Breeder

The easiest and most effective way to get a rat’s age is to ask the breeder and, in fact, this can give you an insight into the kind of breeder that they are.

A reputable breeder should have written records that enable them to give you an accurate idea of the rat’s age and lifespan.

A “feeder breeder”, on the other hand, may not have any such records and may be forced to give you a guess at the rat’s age. We don’t recommend buying from feeder breeders as it can perpetuate cruelty.

Obviously, if you are thinking about adopting an abandoned pet rat – you may not be able to ask the breeder at all.


We hope that our guide on how to tell how old a rat is (with examples) has been helpful in guiding you on how to determine the age of your rat (or potential rat).

As you can see, when rats are young it is relatively easy to tell how old they are but as they mature it becomes much more challenging. It is always best to buy rats at about 6 weeks old as this will ensure they are ready to leave their mothers and are at the right age to become great pets.

Darren Black

I'm Darren Black, the owner, and author of I am from Scotland, United Kingdom and passionate about sharing useful information and tips about properly caring for an animal's wellbeing.

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