There are usually five to seven mouselings in one litter. House mice have a gestation period of only 18 to 21 days. That means that the young take only 18 to 21 days to develop in their mother's uterus. They are born blind and hairless but are ready to go out on their own before the next litter comes. The female mates again shortly after the young are born.
Female mice take only a month or two to grow up and have their own young.
If there is good food and shelter, they grow up faster. Males take from 7 to 11 weeks to mature. Without predators or animals that eat them, the number of house mice would explode.