Does protein powder go bad?

It degrades slowly rather than spoiling. Sealed and kept cool, dry, and out of sunlight, most protein powders stay good well past a year, and the "best by" date is a quality guide, not a hard cliff. The real enemies are moisture and heat: a tub that got damp can clump or grow off-flavors, and that is a genuine reason to discard it. Practical storage is the whole answer — airtight, cool, dry, scoop with dry hands. If a powder smells or tastes off, trust that over the date; otherwise, sensible storage protects both the product and your dollars-per-serving math.