The frequency with which someone can donate blood depends on the type of donation. For whole blood donations, individuals are typically eligible to donate every 56 days, or about every two months. For platelet donations, the waiting period is usually shorter, allowing donors to give every 7 days, up to 24 times a year. Plasma donors can often donate every 28 days. These guidelines are in place to ensure that donors have adequate time to replenish their blood supply and remain healthy. It is important for donors to follow these recommendations and consult with blood donation organizations for specific eligibility criteria.