Hi, here's something that you may consider useful:
Regardless of how much mg your calcium vitamins have, your body will not absorb more than 500, maybe even 400 at a time. If so, your body will disregard the rest.
It's why it's recommended to take the calcium twice a day or even three times (depending on the dr's recommendation but no more than about 1200/day)- once in the am and the other in the evening.
You need vitamin D to help the calcium pass through your gut and into your blood stream- it is then that the calcium can beadsorbed
Every body is different. The metabolism and the body's alkaline is different. If your body is more acidic, then you have better absorption of calcium, if not, just eat an orange or grapefruit or just take the vitamin D to help the body absorb the calcium.
There are so many thing the body needs like your Bs bc your body doesn't make it or how about our age factor---- the older we get the less enzymes our body creates.