Thorne Calcium
vs
21st Century Calcium Citrate +D3 Maximum
Supplement Comparison

  • Calcium: 21st Century Calcium Citrate +D3 Maximum has 2.5× more
  • The image below shows:
    • Side-by-side charts with label nutrient amounts, per serving
    • Nutrient forms as listed on the label
    • 4 nutrients compared
Bar chart: per-serving label amounts and listed forms for Thorne Calcium vs 21st Century Calcium Citrate +D3 Maximum.

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Frequently asked questions

Which active ingredients does Thorne Calcium have?

  • Calcium appears as DiCalcium Malate

Which active ingredients does 21st Century Calcium Citrate +D3 Maximum have?

  • Vitamin D appears as Cholecalciferol (D3)
  • Calcium appears as Calcium Citrate

Which categories do Thorne Calcium and 21st Century Calcium Citrate +D3 Maximum belong to?

  • Single Mineral

What health concerns do Thorne Calcium and 21st Century Calcium Citrate +D3 Maximum address?

  • Joint & Bone Health
  • Women's Health

Which product has a higher amount of Calcium per serving?

  • 21st Century Calcium Citrate +D3 Maximum has the highest total amount of Calcium: 630 mg per serving

How do the serving sizes compare between the two supplements?

  • Serving size:
    • Thorne Calcium: 1 capsule
    • 21st Century Calcium Citrate +D3 Maximum: 2 tablets
  • Calcium
    • This supplement has 250 mg
    • Recommended Dietary Allowance in men: 1000 mg
    • Recommended Dietary Allowance in women: 1000 mg
    • Tolerable Upper Intake Level: 2500 mg
  • Vitamin D
    • This supplement has 500 IU
    • Recommended Dietary Allowance in men: 600 IU
    • Recommended Dietary Allowance in women: 600 IU
    • Tolerable Upper Intake Level: 4000 IU
  • Calcium
    • This supplement has 630 mg
    • Recommended Dietary Allowance in men: 1000 mg
    • Recommended Dietary Allowance in women: 1000 mg
    • Tolerable Upper Intake Level: 2500 mg

Last updated: January 29, 2026

  • Sources & Methodology: Nutrient data and forms are taken directly from Supplement Facts labels. Reviewed and standardized by the VIOscan Research Team. Learn more on the Methodology page.
  • We show the Recommended Dietary Allowance (RDA) when available. If no RDA exists, we show the Adequate Intake (AI). Tolerable Upper Intake Levels (UL) are used for upper limits. Unless otherwise noted, RDAs shown correspond to healthy adults aged 19–50 years and are sex-specific. Separate values exist for 51–70 years and >70 years, and pregnancy and lactation are excluded. All values come from the Dietary Reference Intakes (DRIs) published by the National Academies of Sciences, Engineering, and Medicine (NASEM), Food and Nutrition Board (FNB).
  • Transparency: We’re funded by our users. We don’t have sponsors or affiliate links, and we don’t sell supplements.
  • Editorial standards: we provide independent, impartial and objective data analysis.
  • This analysis is for educational purposes only. It is not a substitute for medical advice.
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  • See an error? Report it through our Contact page.
  • Author: VIOscan Research Team