Ketchup lasts for six months in the refrigerator after the package is opened, or for one month outside of the refrigerator. It does not need to be refrigerated prior to opening.
Ketchup is shelf-stable prior to opening and for a limited amount of time after opening due to its high acidity, but ketchup manufacturer Heinz recommends that opened bottles of ketchup be refrigerated. Refrigerating ketchup does not affect its taste or texture; it merely extends the shelf life of the product. Ketchup bottles do not always carry an expiration date, and even ketchup bottles with a later expiration date should be discarded six months after opening.