Cats should be spayed when they are still quite young, at or before reaching 6 months in age. The minimum age for spaying a cat is eight weeks old. Any cat undergoing spaying should weigh at least two pounds, to lessen the risk of surgical complications.
Cats that are not spayed have an increased chance of contracting cancer. There are also behavioral concerns, like fighting with other animals and spraying urine, which can be nipped in the bud by spaying the animal before it has become sexually mature. Cats that are spayed at 8 weeks do not differ much in outcome from cats that are spayed at 6 months; however, first heat in cats can occur as young as 4 months in age, so spaying female cats as early as possible is recommended. There is no particular reason to wait to spay if the animal is of sufficient body weight.