Calcium Citrate vs Calcium Carbonate Labels: Elemental Calcium, Serving Size, %DV and Added Nutrients
Calcium citrate and calcium carbonate are two compounds that supply calcium in supplements. On a label, the difference shows up in four places: the form name in parentheses, the serving size needed for the printed calcium amount, the other ingredients, and any extra rows such as vitamin D or magnesium. This guide reads three NOW Foods labels from the NIH Dietary Supplement Label Database (DSLD): Calcium Citrate tablets, Calcium Citrate Pure Powder and Calcium Carbonate Pure Powder.
Short answer: the milligram figure next to “Calcium” is the calcium itself, not the weight of the citrate or carbonate compound. All three NOW labels print 600 mg of calcium per serving at 46% DV. What changes is how much tablet or powder carries that 600 mg, and what else sits in the panel.
Where the form name appears
FDA rule 21 CFR 101.36(d) says the source ingredient “may be identified within the nutrition label in parentheses immediately following or indented beneath the name of a dietary ingredient and preceded by the words ‘as’ or ‘from'”, and its own example is “Calcium (as calcium carbonate)”. NOW uses the “from” wording. Its tablet panel reads “Calcium (from Calcium Citrate) 600 mg”, per the DSLD record for the 250 tablet bottle.
The two pure powder records list “Calcium 600 mg” as the only row, with the form given in the product name: Calcium Citrate Pure Powder and Calcium Carbonate Pure Powder.
Elemental calcium vs compound weight
The NIH Office of Dietary Supplements calcium fact sheet puts it this way: “calcium carbonate is 40% calcium by weight, whereas calcium citrate is 21% calcium.” The same page adds: “Elemental calcium is listed in the Supplement Facts panel, so consumers do not need to calculate the amount of calcium supplied by various forms of calcium in supplements.” (NIH ODS, Calcium Fact Sheet for Health Professionals)
Our magnesium label guide covers the FDA rule behind this, which uses calcium and calcium carbonate as its example. The short version for calcium: “Calcium 600 mg” means 600 mg of calcium, whichever compound supplies it.
You can see the weight difference on the two NOW powders. Both print 600 mg of calcium per serving. The carbonate powder’s serving is 1/2 level teaspoon, listed as 1.7 g. The citrate powder’s serving is 1 1/2 level teaspoons, listed as 3 g. By our arithmetic, the citrate serving weighs about 1.8 times the carbonate serving for the same printed calcium.
%DV: the same 1,300 mg base
The Daily Value for calcium is 1,300 mg for adults and children 4 years and older, in the table in 21 CFR 101.9(c)(8)(iv). By our arithmetic, 600 mg divided by 1,300 mg is 46%, which matches all three NOW panels. The form does not change the %DV. Only the milligrams of calcium do.
Tablets or scoops per serving
- Citrate tablets: serving size 2 tablets, 125 servings per 250 tablet bottle, per the DSLD label. NOW also sells a 100 tablet bottle with the same panel (DSLD 210410).
- Citrate powder: 1 1/2 level teaspoons (3 g), 8 oz (227 g) bag.
- Carbonate powder: 1/2 level teaspoon (1.7 g), 12 oz (340 g) bag.
Check the serving size line before comparing two bottles. A label that lists 600 mg per 2 tablets and one that lists 300 mg per tablet carry the same calcium per two tablets.
Added vitamin D, magnesium and other minerals
The NOW Calcium Citrate tablet is not calcium alone. Its panel per 2 tablets, from the DSLD label image:
| Row | Amount | %DV |
|---|---|---|
| Vitamin D (as D2 ergocalciferol) | 10 mcg (400 IU) | 50% |
| Calcium (from calcium citrate) | 600 mg | 46% |
| Magnesium (from magnesium oxide and magnesium aspartate) | 300 mg | 71% |
| Zinc (from zinc chelate complex) | 15 mg | 136% |
| Copper (from copper chelate complex) | 1 mg | 111% |
| Manganese (from manganese chelate complex) | 5 mg | 217% |
The two pure powders list calcium only. If you also take a multivitamin, its panel may list some of the same rows. Our multivitamin label guide shows how those rows are printed, and a pharmacist can look at the totals across everything you take.
Calcium carbonate in a citrate tablet
The tablet’s other ingredients read: “Hydroxypropyl Cellulose, Vegetarian Coating [hypromellose (cellulose), calcium carbonate, glycerin], Croscarmellose Sodium, Silicon Dioxide, Magnesium Stearate (vegetable source) and Stearic Acid (vegetable source).” So calcium carbonate appears in the coating list, while the panel row names calcium citrate as the source of the 600 mg. The older 100 tablet record lists “Vegetarian Coating” without the bracketed parts (DSLD 210410).
Directions, as the labels print them
Read the directions word for word rather than assuming one rule for each form. The labels say:
- Citrate tablets: “Take 2 tablets daily, preferably in divided doses, with food.”
- Citrate powder: “Take 1 1/2 level teaspoons daily, with a meal.”
- Carbonate powder: “Take 1/2 level teaspoon daily, preferably with a meal.”
All three also print: “Caution: For adults only. Consult physician if pregnant/nursing, taking medication, or have a medical condition. Keep out of reach of children.”
Marks and allergen lines
The tablet label shows a Non-GMO box, the words Vegetarian/Vegan, a Triangle K kosher mark and a GMP Quality Assured seal. Its allergen line reads: “Not manufactured with wheat, gluten, soy, milk, egg, fish, shellfish or sesame ingredients. Produced in a GMP facility that processes other ingredients containing these allergens.” The carbonate powder record also lists a Non-GMO Project Verified mark.
The front of the tablet label carries structure/function statements marked with an asterisk, and the label says: “These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure or prevent any disease.”
Side by side
| Label line | Citrate tablets | Citrate powder | Carbonate powder |
|---|---|---|---|
| Serving | 2 tablets | 1 1/2 tsp (3 g) | 1/2 tsp (1.7 g) |
| Calcium | 600 mg, 46% DV | 600 mg, 46% DV | 600 mg, 46% DV |
| Other panel rows | D2, magnesium, zinc, copper, manganese | None | None |
| Size | 100 or 250 tablets | 8 oz | 12 oz |
Label checklist
- Find the “as” or “from” words to see the compound.
- Use the milligrams next to “Calcium” to compare, not the compound name.
- Read the serving size: tablets, capsules or teaspoons.
- Scan for extra rows such as vitamin D or magnesium.
- Read the directions and caution lines word for word.
For the rest of the panel, our supplement label guide walks through each section. The tablet has its own page: NOW Calcium Citrate tablets.
FAQ
Does 600 mg of calcium citrate mean 600 mg of calcium?
On a Supplement Facts panel, the number next to “Calcium” is the calcium. NIH ODS says elemental calcium is listed in the panel, so you do not need to convert it.
Why is the citrate serving bigger?
NIH ODS says calcium citrate is 21% calcium by weight and calcium carbonate is 40%. On the NOW powders, the citrate serving is 3 g and the carbonate serving is 1.7 g for the same 600 mg of calcium.
Does the form change the %DV?
No. %DV is based on the 1,300 mg Daily Value for calcium in 21 CFR 101.9, so 600 mg reads 46% for either form.
Talk to your doctor or pharmacist before starting calcium or any supplement, especially if you take medication or other products that list calcium, vitamin D or minerals.
These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease.