How can you tell if baking powder is still fresh?

Perhaps you’ve had this container of baking powder sitting in your pantry for a while. How can you determine if it is still fresh and ready to be used in your next baking project?
Place ½ teaspoon in a small bowl, add ¼ cup of hot water, and see whether or not it foams.

If so, keep it.

If not, toss it. In general baking powder will last for 6-12 months in your pantry.
Linked to: NourishingJoy, HomemakerOnADime