Hamsters become fertile at different ages dependent on their species, but this can be from one month to three months of age. Male hamsters remain fertile for the rest of their lives, though females do not. Females are in heat approximately every four days.
Breeding season is from April to October, with two to five litters of 1 to 13 young being born after a gestation period of 16 to 22 days. Gestation lasts 16 to 18 days for Syrian hamsters, 18 to 21 days for the Russian hamsters, 21 to 23 days for Chinese hamsters and 23 to 30 for Roborovski Hamsters. The average litter for Syrians is about 7, but can be as great as 24, which is the maximum number of pups that can be contained in the uterus. Campbell's Dwarf Hamsters tend to have 4 to 8 in a litter but can have up to 14. Winter White Russian Dwarf Hamsters tend to have slightly smaller litters, as do Chinese and Roborovski hamsters.