A female cat can usually go into heat and become pregnant between one and two months after having her litter. In some cases, the duration between pregnancy and estrus, or heat, can be as little as one week.
Cats are polyestrous, meaning that they have multiple heat cycles per year. The age at which a female cat first goes into heat varies, but it can be as little as 5 months of age in breeds such as the Siamese. Many long-haired breeds become fertile at 10 months or older. Several factors influence a female cat's heat cycle, including the environmental temperature, the length of daylight and the presence of other cats. In the northern hemisphere, cats typically mate between March and September.