Swanson Premium Brand's Calcium supplement provides 500mg of elemental calcium from a combination of Calcium Ascorbate, Citrate, and Carbonate, aiming to offer varied absorption profiles. Calcium Citrate is generally well-absorbed, even without food, making this a more versatile option than pure calcium carbonate. However, a significant deficiency is the absence of Vitamin D3, a fundamental nutrient that facilitates calcium absorption in the gut and its proper incorporation into bones. Without D3, a substantial portion of the ingested calcium may not be effectively utilized by the body, limiting its overall efficacy for bone and general health, despite its attractive price point.