Mouse Gestation Period: How Long Is a Mouse Pregnant?

How long is a mouse pregnant?

A mouse carries her pup for an average of 20 days, or about 0 months and 2 weeks. Counting from the breeding date, birthing is normal anywhere from day 19 to day 21.

Key checkpoints across the 20-day mouse gestation, measured in days from breeding:

Estimate your mouse's birthing date

Enter the breeding date for an estimated birthing date at 20 days.

Open the full Mouse gestation calculator

Mouse gestation stages, month by month

Signs a mouse is pregnant

• Weight gain from about day 8, detectable on a small digital kitchen scale
• Pear-shaped abdomen from roughly day 12, very obvious by day 16
• Nipples become visible through the coat in the second week
• A covered, carefully built nest appears in one corner

Signs of approaching birthing

• Increased eating and drinking through the second half of the pregnancy
• She becomes defensive about the cage being opened in the last days
• Contact your vet if labour stalls, if the animal strains without progress, or if there is abnormal discharge before birthing begins.

What affects mouse gestation length

• At 19 to 21 days, mice have one of the shortest and most reliable gestations of any mammal kept as a pet.
• A doe can conceive again within 24 hours of giving birth and can produce a litter every three weeks, which is why an un-separated male leads to dozens of mice within months.
• Young mice reach sexual maturity at around five to six weeks, so a mixed litter left together will start breeding among itself before it is fully grown.
• Pups are born hairless, blind and deaf at roughly one gram — about the weight of a paperclip — and are entirely dependent for two weeks.
• Mice are far more sensitive to nest disturbance than rats: cleaning the cage or handling pups in the first week frequently causes the doe to abandon or eat the litter.
• Females housed in groups often nurse each other's pups communally, which improves survival but makes litter parentage impossible to track.

Mouse gestation chart

Every fifth breeding date across the year with the matching birthing date, calculated at 20 days. Find the row closest to the date the mouse was served; because normal gestation spans 19 to 21 days, plan for a window of a few days either side. Filter by month, or print the chart for the barn wall or breeding record: navigation, buttons and adverts are hidden on paper.

Sources for mouse gestation figures

Figures on this page are drawn from laboratory mouse husbandry standards, fancy mouse breeder records and small mammal veterinary guidance, and checked against the references below. Averages describe healthy animals under normal management; individual animals vary, and nothing here replaces advice from your vet.

• The Jackson Laboratory — mouse breeding resources
• Merck Veterinary Manual — reproduction and pregnancy chapters by species
• Laboratory animal science references on rodent reproduction