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Home > Rodents > At What Age Do Mice Reach Sexual Maturity? What To Know!

At What Age Do Mice Reach Sexual Maturity? What To Know!

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Mice are small creatures that are members of the rodent family. They are found in the wild and commonly kept as house pets. These “fancy” mice are the same species as wild mice but are usually tamer and have different fur colors. Mice of both the fancy type and wild type reach sexual maturity at 6 to 8 old.


How Can You Tell a Mouse Has Reached Sexual Maturity?

It’s challenging to tell when your mouse has become sexually mature without laboratory testing, apart from seeing them physically mate with each other. It’s safe to assume that male and female mice have reached sexual maturity at 6 weeks. It’s easier to tell their sexes and separate them accordingly.

Male mice have a larger distance between their anus and genitalia, or anogenital distance (AGD). They also often have a visible penis. Female mice have a smaller AGD.

How Can You Tell If a Mouse is Pregnant?

Pregnant mouse foraging for food
Image By: colin robert varndell, Shutterstock

Because mice are quick and relatively shy creatures (they’re nocturnal, being most active at night), it can be tricky to determine whether your mouse is pregnant in the early stages. If you’ve seen your mice mating, the female is probably pregnant. Mice are incredibly fertile; a female mouse’s estrus cycle only lasts four to five days and continues again from the fifth day.

Another sign that your mouse might be pregnant is the presence of a plug. A plug is old semen that a mated mouse holds in her vagina for up to 48 hours past mating, after which time it usually falls out. This plug can sometimes be seen in the cage after it’s fallen out.

Pregnant mice grow larger, as all pregnant female mammals do when carrying babies. A mouse pregnancy lasts around 20 days; during this time, her belly will swell outwards as her litter grows inside her.


How Many Pups Does a Mouse Have?

newborn mice
Image By: Live and Learn, Shutterstock

Mice can have up to 12 pups in a single litter, but the average is around five or six. Mice can have almost 15 litters in 12 months, meaning you could end up with 180 mice running around in a single year! Therefore, separating female and male mice is important when they reach sexual maturity.

How Soon Can a Mouse Get Pregnant After Giving Birth?

Mice have a very rapid reproduction cycle, which allows a female mouse to get pregnant only 24 hours after giving birth to a litter. Because mice gestate their offspring for 19–21 days on average, they can quickly produce large numbers of babies. Each mouse will reach reproductive maturity at around 6 weeks, so the number of mice can quickly get out of hand.

To compare, humans gestate their babies for 40 weeks on average and usually only have one baby at a time.

When Should You Separate Male and Female Mice?

Female and male mice should be separated when they reach sexual maturity to prevent unintended litter.



Mice (like other rodents) reproduce quickly in large volumes to ensure their survival. Both male and female mice reach sexual maturity at around 6 to 8 weeks of age, which is the best age to separate them to prevent unintended litters. If you think your mouse is pregnant, take them to a veterinarian who can treat rodents. They can determine whether or not she’s pregnant and estimate how far along in the pregnancy she is.

Featured Image Credit: Ralphs_Fotos, Pixabay

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