A pregnant mouse can give birth to six to 12 babies in one litter. A female mouse can become pregnant several times a year. One mouse couple can produce 40 or more babies in one year.
Each baby mouse reaches sexual maturity and begins producing its own offspring within less than a year of being born. With so many baby mice being born and growing up so quickly, the mouse population in one area increases by the thousands every year. Female mice are pregnant for less than a month, which makes mice some of the fastest-breeding animals in the world.