21st

21st Century Calcium 600 mg Supplement

Calcium

4.7/ 5 on Amazon6,495Amazon ratings5,000+bought last month2.7ProductDome score

Better rated than 63%
More reviewed than 82%

Limited evidenceLast refreshed Aug 4, 2026Amazon data + ProductDome analysis · methodology

Best forYou want a plain, high tablet count calcium carbonate supplement.

For a plain calcium carbonate tablet with a long supply, this delivers the basics without added extras.

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ProductDome scorecard

How it ranks among the 107 calcium we track

2.7/ 5ProductDome scoreLimited evidence

Owner satisfaction · 56% of scorecategory median 4.6★4.7

4.7★ across 6,495 Amazon ratings, Bayesian-smoothed toward the category average.

Evidence strength · 17% of scorecategory median 1,800 ratings4.8

6,495 Amazon ratings, weighted on a log scale so huge counts don't drown everything.

Buyer demand · 11% of score5.0

5,000+ bought on Amazon last month.

Data quality · 11% of score2.5

Brand identity, imagery, description and spec coverage.

The ProductDome score is separate from the Amazon rating shown above: it combines the Bayesian-smoothed Amazon rating with evidence volume, tracked demand, and data quality across the 107 calcium we track - how the scorecard works · full calcium data report. Confidence: limited - incomplete product information.Last refreshed Aug 4, 2026. Data-computed, not a hands-on test. Compiled by the ProductDome Research Team.

Overview

21st Century's calcium carbonate tablet provides 600 mg of calcium per tablet, 400 tablets per bottle, formulated vegan-friendly, non-GMO and gluten free for general bone strength support in men and women.

Calcium carbonate is the most concentrated and typically least expensive form of calcium, but it is best absorbed when taken with food since digestion relies on stomach acid. No listing details point to added vitamin D or magnesium in this particular formula.

600 mg calcium carbonate per tablet
400 tablets per bottle
Non-GMO and gluten free
Vegan-friendly formula

Who it's for

For people who want a plain, no-frills calcium tablet for general bone support and do not need it combined with vitamin D or magnesium. Not for those wanting a combination bone-health formula in a single tablet.

Strengths and trade-offs

Drawn from this product's published specifications.

What stands out

400-tablet count offers a long supply
Non-GMO and gluten free

What to check first

No added vitamin D or magnesium in this formula
Best absorbed only with food

Performance notes

Calcium carbonate delivers a high percentage of elemental calcium per tablet but works best when taken alongside a meal, since the body needs stomach acid to break the compound down for absorption.

Specifications

Brand	21st
Model	27534

How it compares

This product against the closest alternatives we track in calcium.

Product	Amazon rating	Ratings	ProductDome score
21st Century Calcium 600 mg SupplementThis product	4.7 / 5	6,495	2.7 / 5
Nature Made Calcium Magnesium Zinc with Vitamin D3NATURE	4.8 / 5	19,900	4.7 / 5
Nature's Bounty Calcium Magnesium & Zinc CapletsNature's	4.7 / 5	23,000	4.6 / 5
Caltrate 600 Plus D3 Calcium and Vitamin D Supplement TabletsCaltrate	4.7 / 5	16,400	4.6 / 5
Citracal Slow Release- Calcium 1200 mg with Vitamin D3Citracal	4.7 / 5	11,909	4.6 / 5

Frequently asked

Questions about the 21st 27534

Common buyer questions answered straight from the product spec data - no fluff, no "it depends".

How much calcium is in each 21st Century Calcium tablet (model 27534)?

Each tablet provides 600 mg of calcium as calcium carbonate.

How many tablets come in a bottle of 21st Century Calcium?

The bottle contains 400 tablets.

Is 21st Century Calcium vegan-friendly?

Yes, it is marketed as a vegan-friendly, non-GMO and gluten free formula.