Sexing Baby Rats: Boy or Girl? How To Tell The Difference Quickly

If you are planning on breeding pet rats, you will need to know how to sex a baby rat accurately. This is an important skill because rats are prolific breeders who become sexually mature as earlier as 5 weeks of age. Is your rat already pregnant? Get a head start!

Ancestral ties aren’t important to rats, meaning they will breed with their siblings and parents if given the opportunity. The health and well-being of your baby rats and the quality of their genetics will be compromised if the pregnancy is a result of inbreeding.

Keep reading to learn how to sex a baby rat quickly and accurately.


When Can You Sex A Baby Rat?

You can see physical differences in baby rats within the first couple of days following birth, if you know what to look for. Most people can spot the difference between a male and female baby rat by the third week because that is when the scrotum becomes more visible on males.


Separate Males And Females At 5 Weeks

Rats become sexually mature as early as 5 weeks of age. This is why it’s important to sex baby rats between the third and fourth week, so you can be ready to separate the boys and girls by the start of their 5th week.

The female babies can stay with their mom, but the male babies will need to be moved to another cage. It’s recommended that you keep same-sex siblings together until 6 weeks of age to finish developing their social skills. After 6 weeks, the kittens are ready to go to their new home.


How To Sex A Baby Rat Earlier Than 3 Weeks

How to sex a baby rat

Some people accurately sex their baby rats as early as five days old. The easiest way to sex a baby rat during this stage of development is to compare the undersides on each baby. The distance between the genitals and anus will be shorter on the female baby rats than the male baby rats.

When you are first starting out, it’s recommended to re-check each baby if you sexed them before turning 3 weeks old. It’s easy to make a simple error when sexing a baby rat for the first time and you don’t want to be stuck with an accidental litter.


Sexing A Rat After 3 Weeks

After the third week, the task of sexing baby rats becomes much easier. This is mostly in part to the scrotum developing and becoming more of a prominent feature on male babies, but you might notice other gender-specific differences too, like nipples on the female babies.


Physical Differences

Besides the difference in genitalia, there is usually a noticeable size difference between male and female baby rats, but it sometimes takes until they reach maturity before the difference becomes more obvious to the unfamiliar eye.


Behavioral Differences

Once the baby rats become mobile, you might notice a difference between activity levels for the genders. Female baby rats are typically more curious about their environment, so they will spend more time exploring than their male counterparts. Although males can be curious too, they are more likely to spend time relaxing or cuddling with you.



If you are going to start breeding pet rats, you need to know how to accurately sex baby rats before they reach sexual maturity and take the steps to separate them. This will help you avoid unplanned litters before they become a problem and stop instances of inbreeding from occurring.

Rats are wildly underrated pets, but there’s a lot to know before you start breeding them – if that’s your plan. It’s something you do out of love, you aren’t going to make a fortune, so if you don’t genuinely love having a lot of rats around and meeting other people who love rats, this might not be the best idea.


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