If you are wondering about the actual shelf life of the concentrate itself, this depends on many factors, such as quality, storage, and material. In theory, the concentrates should last indefinitely if packaged and stored properly, but could expire rather quickly if improperly packaged. If you are wondering how many hits your concentrate pen will last, that is like asking how many licks it takes to get to the center of a tootsie pop. It depends on many factors-- how often you smoke, the size of your hits, the duration of your drags, etc.