Just like humans, from newborn to senior, we don't always get all the vitamins, minerals, and calcium we need in our day to day lives to be healthy.
This also applies to our beloved Bearded Dragons. While some people say calcium isn't needed everyday, I have to completely disagree with that.
There is no such thing as to much calcium for dragons, any excess will be expelled through their urates (urine sac, the white bag that you see attached to their poo).
I have tried virtually every calcium supplement available and the only one I can recommend is the Rep-Cal Calcium with Vitamin D3, the one with the pink label.
Here is a list of the Calcium powders carried by most pet stores, and my experience with them.

Company 

 Brand 

 Picture 

 My Opinion

Rep-Call

Calcium with vit. D3

- Superfine powder
- A pinch will do
- Sticks to food
- No clump
- Last a long time
- Can be used to treat MBD

Zoo Med

Repti Calcium with D3

- Clumps
- Doesn't stick to food
- Requires allot
- Can't be used to treat MBD

Exo-Terra

Calcium + D3

- Fine powder
- Doesn't stick to food
- Spasms development
- Just a horrible product
- They need to stick to aesthetically pleasing structures
- Can't be used to treat MBD

Flukers

Calcium with D3

- Fine powder
- Falls off food super easily
- Melts like powdered sugar 
- Clumps so bad
- Doesn't help with MBD

With my use of all of these I can confidently say that Rep-Cal is the right choice when it comes to calcium or any supplements for dragons.
Using the others, I noticed early signs of MBD (Metabolic Bone Disease) with muscle spasms, toe twitches while at rest and muscle loss.
The moment I put them one Rep-Cal all signs disappeared. This is why I believe so much in their supplements, it does what it's suppose to do.

Calcium isn't the only supplement Beardies need. I'm sure you've seen the pellet food in the pet stores and wondered if your dragon will eat it.
Well, some dragons might eat it, some might not. Just like the calcium powders, there are quite a few options for pellet foods. I'll tell you the one I use and how I use it. 

These pellet foods are meant to be moistened with water before being offered to your beardy as the hard pellet will hurt their teeth and may break them.
Moistening them will allow for hydration while providing nutrition. Of course this is assuming your dragon is actually interested in it, I know mine never have.
I'm not going to list all the available ones like I did with the calcium because there is only one that should be used, just like the calcium. Yes, it's Rep-Cal, they are just that good when it comes to supplement.

The way I get this stuff into my dragons, since they have no interest in it moistened or dry, is by gut-loading crickets.
Crickets eat everything, so why not feed them something that will be extremely beneficial to your dragon?
You feed this to your crickets, then feed your crickets to your dragon, it's that simple.
You also have to realize that when you buy your crickets they aren't gut-loaded with anything of nutritional value. Feeding crickets bought from the pet stores right away is like you eating a cardboard box or McDonald's, yes, it might fill you up, but you get absolutely no nutritional value from it. So when you buy your crickets, feed them this 24 hours before feeding them to your beardy. This will allow for optimal nutrition.

Once they hit their mid life, or aren't looking too healthy, you may want to look into adding a vitamin supplement to the Shake & Baked crickets and to the salad.
The one I use, and matches up nicely with the calcium and the pellet food is once again, Rep-Cal.

 

This multivitamin has everything that is needed to maintain a healthy beardy. I don't really need to go into much details on this since it's self explanatory. 

So if you have all three of the Rep-Cal supplements, Calcium, Pellets and Multivitamin, you're looking at having a perfectly healthy Bearded Dragon that will be happy and energetic for years to come.