The shelf life of whey protein powder depends on several factors such as the quality of ingredients, processing methods, and storage conditions. On average, unopened whey protein powder can last for about 12-24 months when stored in a cool, dry place. Once opened, it is recommended to use the powder within 3-6 months for optimal quality. To extend the shelf life, it is important to store the powder in an airtight container, away from direct light and heat, and to minimize exposure to moisture. Regularly checking the powder for signs of spoilage, such as an off odor or discoloration, is also recommended.