Ketchup Catsup Facts

Ketchup (or catsup) can go bad, because of the acidity of the tomatoes and vinegar, and the amount of sugar.

An unopened container of ketchup can remain stored for up to two years past the printed expiration date.

Once the bottle is opened, it will last for another year in the refrigerator. If you keep your ketchup at room temperature, the shelf life for an opened bottle in your pantry is about a month, though you should check for signs of spoilage before consuming the ketchup.
As ketchup ages, the vinegar and other liquid will begin to separate out from the tomato paste in the condiment. You have likely experienced the beginning stages of this when you go to squeeze out some ketchup, and find a splash of liquid instead.