Unpopped popcorn does not typically have an expiration date. Instead, manufacturers usually stamp it with a "best by" date to indicate the date on which freshness can start to deteriorate.
The shelf life of popcorn beyond its best buy date depends on its state and how it is stored. Loose popcorn kernels can last indefinitely if placed in an airtight container and stored in a cool, dry cabinet, while microwave popcorn only lasts six to eight months before becoming stale. Popped popcorn may last up to two weeks.
Indications that unpopped popcorn may have passed its prime include dark kernels and kernels that will not pop, and microwave popcorn that is not fresh may emit a rancid smell.