So, does baking powder have an expiration date? Well, sort of. Most baking powder containers come with a "best by" date, which indicates how long it'll remain potent.
Baking Powder Gone Bad at Paul Gorman blog
But, in reality, baking powder can last for months or even years if stored properly. It's all about the conditions - if you keep it cool, dry, and away from light, it'll stay fresh for a long time.
That being said, if you're using baking powder that's past its "best by" date, you might notice that your baked goods aren't rising as well as they used to. This is because the leavening power has decreased, resulting in a denser final product.
