Can a recently neutered cat still impregnant?

Question
my male cat was just neutered this past monday [4 days ago] and today he decided to try and mate with my unspayed female.what are they chances that he may have any sperm and able to get her pregnant? i know that it is probably impossible,but i just want to make sure.

Answer
Hi Nicki,

Unfortunately, yes, there is that possibility.  The vet should've informed you of this, as they can still be fertile for approximately 3-4 weeks after being altered if neutered after they have begun sexually maturing.  I do not have personal experience with this as all of my six cats as well as fosters were altered before reaching 5 months old.  You should keep them separated for at least three weeks after the date he was neutered, probably four to be on the safe side.  

For future reference, it is important to neuter/spay before cats begin sexually maturing, so a good rule of thumb is by four months old.  It is safe and actually best to alter cats that are between 8 weeks and 3 months old that weight at least 2 pounds and have not been sick in the past week (to ensure their immune systems are healthy).  Studies have shown that cats/kittens recover better and faster when altered at this stage.  I highly recommend getting your female spayed as soon as possible.  I wish you all the best, and please let me know if you have any more questions!

Best regards,
Holly Martin