When should you spay or neuter you dog or cat?

I need to know how many weeks after your puppy or kitten is born  before you spy or neuter them. I know that you spay females and neuter males but I am doing a project an d need to know now!
:-)Kittens and puppies can be spayed or neutered once they're two pounds in weight and eight weeks in age.  Sadly some shelters and vets are still behind the times and waiting until animals are six months in age.  And a lot of those adopting animals that are supposed to bring them back for the procedure "when they're old enough" fail to do so and let them breed.  Hopefully ALL shelters will start using the early spay/neuter method so animals won't go out unless they're already desexed.Normally around 5 to 6 months!!Thats a question with a lot of different answers.

At the animal shelter I work at, we neuter males at 9 weeks and females at 12 weeks.

For a personal pet, its often better to wait till the animal is 6 months or so. Some breeds, most notably giant breeds, should not be fixed until they are completely mature.

Here is some information describing the pros and cons of early spay neuter

http://www.caninesports.com/SpayNeuter.h...I have always heard 6 months is that "magic" number for spaying and neutering.  Although, there is research that shows that spaying (a female) before the first heat prevents the development of mammary gland tumors. Since females can go into heat as young as four months of age, they should be spayed before then to receive that protection.  Males on the other hand I am sure 6 months is a good age.http://www.aspca.org/site/PageServer?pag...I think it is when they are like 6 months