This question often refers to supplement forms, but food is the first-line option. When supplements are needed, the choice depends on tolerance, stomach acid status, and total daily intake. Calcium carbonate provides more elemental calcium and is often best taken with meals. Calcium citrate may be advantageous when stomach acid is low (e.g., some acid-suppressing medication users) and can be better tolerated by some. Clinically, “right dose and context” matters more than form: adequate vitamin D, sufficient protein, and exercise make calcium more effective for bone goals. A practical rule is to split doses rather than taking very large single doses, and to avoid unnecessary high totals. If you have kidney stones, kidney disease, or take interacting medications, plan timing and dose with a clinician/pharmacist. Bottom line: the “best” calcium is the one matched to your risk profile and protocol.