If you suffer from acid stomach, it is best to avoid Calcium Citrate.
Calcium Carbonate is alkaline based, it requires extra stomach acid for better absorption, hence it is best taken right after meals or with a glass of acidic juice such as orange juice.
ensure to look for the elemental calcium content, not the total content. For instance, a supplement containing 500mg of Calcium Carbonate provides 200mg of elemental calcium. Hence this pill in this example only provides 200mg of calcium, not 500mg