How old do cats have to be to have kittens?

Domestic and feral cats that are not spayed or neutered can start mating and reproducing when they are between four and five months old. A female house cat can go into heat at four months.

Until she is spayed or becomes pregnant, a female cat repeats the estrus cycle periodically throughout the year, especially during spring, summer and early autumn.

When a female cat is in heat, she may go to great efforts to meet and mate with a tomcat. Signs that a female cat is in heat include increased affection, genital grooming and calling meows. Signs of pregnancy in a female house cat include rosy pink nipples, a vigorous appetite and abdominal swelling at around five weeks. The typical house cat gestation period is approximately 65 days.