How long does Hellman's mayonnaise last after its expiration date?

it doesnt because it has expired is this a trick question?

NOTE: Update by new author: Hellmann's Mayo shows a "Best if used by" date. Not an expiration date. Opened and then closed and then refrigerated jars/packages last a very long time. Some people like to go by expiration dates or best if used by dates but I prefer the old fashioned method.

Open the container; Smell the product; View the product; Taste a small sample; If all are good then it's most likely safe to consume.

In fact, I just had some Hellmann's Mayo from an Easy Out squeeze container that said "Best if Used By: SEP0913" and today is OCT0714!

I opened the container and smelled it. Smelled like normal mayo. I looked at it. It didn't look watery or dark; it looked normal. I squeezed a small amount out onto my finger; felt like normal mayo consistency; tasted it; tasted absolutely fine.

I added it to my tuna fish and had a lovely lunch. :-)

If something doesn't pass all of the above tests, you may wish to discard it.