Days 1–7: early pregnancy
Fertilised eggs implant in the uterus and the embryos begin to develop. Losses are most common now, so keep the mouse on a steady diet and avoid stress, transport and abrupt changes in housing.
Mouse Gestation Period: How Long Is a Mouse Pregnant?
A mouse is pregnant for about 20 days, roughly 0 months and 2 weeks. Normal birthing happens between 19 and 21 days, and a typical litter is 5-8 pups.
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.
Mouse gestation stages, month by month
Days 8–14: mid pregnancy
Growth is steady but the demand on the mother is still modest. This is the practical window for a pregnancy check, routine health care and any change of pen, paddock or enclosure.
Days 15–18: late pregnancy
Most fetal growth happens now. Energy and protein needs rise sharply, the abdomen enlarges visibly and the mother should be gaining condition rather than losing it.
Days 19–21: preparing for birthing
Separate the male before the female gives birth, provide deep bedding and nesting material, and avoid handling the nest in the first week. Watch for nesting behaviour, udder or mammary development, restlessness and loss of appetite in the final days before birthing.
Signs a mouse is pregnant
- No return to heat at the expected interval after mating
- Gradual weight gain and a firmer, rounder abdomen from mid pregnancy
- Appetite increases, often noticeably in the second half of gestation
- A vet can confirm pregnancy by ultrasound or palpation once the mouse is far enough along
Signs of approaching birthing
- Mammary development and nesting behaviour in the final weeks
- Restlessness, reduced appetite and isolation from others in the last day or two before birthing
- 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
- A mouse is pregnant for about 20 days, roughly 0 months and 2 weeks.
- The normal range runs from 19 to 21 days, a window of 2 days.
- A typical litter is 5-8 pups, and larger litters usually arrive slightly earlier than the average.
- Maternal age, body condition, nutrition and season each shift the date by a day or two in either direction.
Estimate your mouse's birthing date
Enter the breeding date for an estimated birthing date at 20 days.
Estimate a mouse due date
Estimated birthing date
Tuesday, 18 August 2026
Earliest
17 Aug 2026
Latest
19 Aug 2026