Carbonate or Citrate?
There is a difference
Calcium occurs in different forms, including calcium carbonate, citrate, gluconate, lactate, dolomite, and coral calcium. Most supplements are made with either calcium carbonate or calcium citrate. The amount of elemental calcium in a supplement is important, because that is the amount of calcium the body can actually absorb from the calcium compound. For example, 1,500 mg of calcium carbonate contains 600 mg of elemental calcium.
Caltrate® is a calcium carbonate product; it's a smaller tablet with a more concentrated form of calcium so you can take fewer tablets to get the recommended amount. And fewer tablets mean your bottle of Caltrate® may last longer.
Compare the two forms:
Calcium carbonate - Caltrate® A concentrated form of calcium, yielding about twice the amount of elemental calcium than equal amounts of calcium citrate.
Calcium citrate A bulkier form of calcium, yielding about half the elemental calcium than equal amounts of calcium carbonate. You need to take more tablets or larger tablets.