This is the recommendation from my endocrinologist who I saw recently for osteoporosis.

I try to get my daily requirement of calcium (minimum of 12mg) from food sources. If I don’t get enough of that in a day I supplement with calcium citrate, approximately 333mg (one tablet in the bottle as 3 tablets equals 1000mg). On my doctor’s advice I take the supplement with a meal as he told me you need your stomach acids to metabolize the supplement with food. He also told me to never take more than 400mg at a time as that is all the body can absorb and metabolize at one time. I also take 1000 units of Vitamin D3 per day.