Is amoxicillin effective after the expiration date?

NO: There is a reason for expiration dates, don't use expired medications.Also if you have some antibiotic left of a prior rx. You did not finished it.

Possibly: The expiration date listed is usually a lot shorter than the actual time during which the drug is effective, but why take the risk? If you really need the antibiotic, get one you are sure works. You also did not say how far out of date it was.