Popcorn kernels that are not popped yet will last for up to 2 years.
You should keep the popcorn kernels in a sealed container if not popping them and they will last up to 2 years.
I've had popcorn kernels that I forgot about in my pantry and they were 2 years old and I thought they were bad but they popped in the popcorn popper just fine.
It's best to use the popcorn kernels as soon as possible and well within a year of buying them but you can still use the popcorn kernels to make popcorn after 2 years.
Microwavable popcorn in the bags that are not popped will last for 3 to 4 months.
Popped popcorn typically lasts for up to a month before it goes bad and stale.