Our DIY HCG has an expiration Month/Year printed on each label of approximately 4 years from the date the HCG is bottled. Theoretically, before opening, if our homeopathic HCG is kept in a cool place away from EMF (electromagnetic fields) it will last indefinitely. However, once the bottle is opened, it will inevitably be contaminated with saliva, air, etc. At this point, it will last at least for a full 40-day round with an estimated opened-bottle shelf life of 6 months. The homeopathic HCG drops may be kept at room temperature during a round. But they will last longer if refrigerated. Therefore, if you have an open bottle that will not be used for a while, you may want to refrigerate it, for example, during a planned break or the break between rounds of HCG.