The problem with supplements of any type, not just calcium, is that our bodies don't always absorb all that we give them- you could be taking 1200mg, but if your body only absorbs 300mg of it, you come up short. With calcium, you also have to look at the type of calcium- carbonate or citrate. Calcium carbonate is cheaper but doesn't absorb as easily, citrate is a little more expensive, but studies show our bodies absorb more of it. I figure if I'm going to take something, I want it to actually help & not get flushed down the toilet
Its also a good idea to spread the amount out through out the day- the body can only absorb so much at one time. I like the vitamin packets I use now because both the daily vitamin & the calcium are in 2 seperate tablets (4 tablets total), so I take a vitamin & calcium in the morning & the other 2 in the evening. At my doctors instruction, I also take an additional calcium supplement- but that's because I have a GI problem that interfers with the amount I can absorb so they would rather I take too much then not enough.