Shop 21st Century Calcium Citrate Plus D3 Maximum Tablets (400-count). This high-bioavailability calcium citrate formula, paired with vitamin D3, supports optimal bone health and density. Each bottle provides a long-lasting supply of 400 tablets for daily calcium and vitamin D3 support.Maximum Strength formula combines calcium citrate with vitamin D3 to enhance absorption and daily bone support. This product is free from artificial flavors, colors, and preservatives.