Calcium citrate is 21% calcium by weight. Calcium lactate is a salt form of calcium carbonate and is around 18% calcium by weight. Both forms are absorbed evenly and not affected by stomach pH and can be taken with or without food. But calcium in the form of carbonate is best to take with meals. Also, supplement only 500mgs of calcium at a time because that’s about all the body can use effectively from one dose. Therefore, if your health professional tells you that you need to add 1000mgs/day of calcium in the form of a supplement, take calcium carbonate in 2-doses: 1 -500mgs tablet with a morning meal and 1 with an evening meal. Make sure your calcium product works synergistically with other supplements to in order to avoid nutrient overages, which are common with typical, indiscriminate supplement use.