There's a "best by" date on my baking soda. I made a honey cake yesterday and it fell after it came out of the oven. Now it has a giant trench in.
Firm resolutions notwithstanding, you probably haven't cleaned out your kitchen cupboards as recently as you'd like. The back corners.
So, does baking powder expire or does baking powder go bad? When properly stored, the shelf life of baking power is actually Indefinite, but.