How many calories are in a calcium supplement?

Most have 0 calories. Most tablets (oscal, citracal) have no calories. Soft chewable froms will typically have a few calories. For examplem, viactiv milk chocolate soft chews have 20 calories.
I think you mean. Milligrams. 1000 mgs are recommended by the gov't as a daily dose from food or supplements. Please get calcium w/co-factors like d, k, boron, etc. So it will work best. Peace and good health.