Corrected Calcium Calculator (Albumin-Adjusted)

Enter total serum calcium and albumin in conventional (mg/dL, g/dL) or SI units (mmol/L, g/L) to get the albumin-corrected calcium, the value in the other unit, and Payne's original 1973 adjustment for comparison.

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Written and reviewed by the Kinase Medical Team · Last reviewed 30 September 2026

Quick Answer

Corrected calcium (mg/dL) = measured Ca + 0.8 × (4.0 − albumin g/dL); in SI units, Ca (mmol/L) + 0.02 × (40 − albumin g/L). Add about 0.8 mg/dL for every 1 g/dL that albumin is below 4.0. The correction is only an estimate — measure ionised calcium in critical illness or acid–base disturbances.

For learning — not for clinical decisions. This calculator is a study aid for exam preparation. Check every result against your institution's protocols and senior advice before acting on it.

Corrected calcium calculator

Units

Enter total calcium and albumin from the same sample.

How it's calculated

Conventional units
Corrected Ca (mg/dL) = Ca + 0.8 × (4.0 − albumin [g/dL])
SI units
Corrected Ca (mmol/L) = Ca + 0.02 × (40 − albumin [g/L])
The same correction converted: 0.8 mg/dL ÷ 4.008 ≈ 0.2 mmol/L per 10 g/L of albumin.
Payne et al. 1973 (original)
Adjusted Ca (mg/100 mL) = Ca − albumin (g/100 mL) + 4.0
Derived from the regression of calcium on albumin in 200 samples; it uses a factor of 1.0 rather than 0.8.

How to interpret the result

Reference ranges from StatPearls (Hypocalcemia, NBK430912). Use your own laboratory's range.
MeasureTypical reference range
Total serum calcium8.5–10.5 mg/dL (2.12–2.62 mmol/L)
Ionised calcium4.65–5.25 mg/dL (1.16–1.31 mmol/L)
Low total Ca that corrects into rangeProbable pseudohypocalcaemia from low albumin — confirm with ionised calcium if it matters
Corrected Ca still low / highTrue hypo- or hypercalcaemia is likely — confirm with ionised calcium

Worked example

A patient with nephrotic syndrome has total calcium 7.6 mg/dL and albumin 2.0 g/dL.

Corrected Ca = 7.6 + 0.8 × (4.0 − 2.0) = 7.6 + 1.6 = 9.2 mg/dL (≈ 2.30 mmol/L) → within the reference range, suggesting pseudohypocalcaemia.

In SI units: 1.90 mmol/L and albumin 20 g/L → 1.90 + 0.02 × (40 − 20) = 2.30 mmol/L.

Payne's original formula gives 7.6 − 2.0 + 4.0 = 9.6 mg/dL.

Limitations and common pitfalls

  • The correction is an estimate. In critically ill adults it often hides true hypocalcaemia; measure ionised calcium when the answer changes management.
  • No correction is reliable in acid–base disturbances, because pH changes calcium binding independently of albumin.
  • Different albumin assays (bromocresol green vs purple) give different results, so a formula derived with one method may not fit another.
  • Keep units consistent: albumin in g/dL with calcium in mg/dL, or g/L with mmol/L. Mixing them gives nonsense.
  • The formula is meant for low albumin; in patients with normal albumin or high calcium, correction has been reported to misjudge calcium status.

Sources

  1. StatPearls — Hypocalcemia (NCBI Bookshelf, NBK430912)
  2. Payne RB et al. Interpretation of serum calcium in patients with abnormal serum proteins. BMJ 1973;4:643 (PMC1587636)
  3. Limited diagnostic utility of albumin-corrected calcium in the ICU: prospective comparison with ionised calcium (PMC13387552)
  4. Derivation and comparison of formulae for the adjustment of total calcium (PMC10213740)
  5. "Corrected" calcium: calcium status underestimation in non-hypoalbuminemic and hypercalcemic patients (PubMed 19654080)

For learning — not for clinical decisions. Reference ranges and cut-offs vary between laboratories and guidelines.

Frequently Asked Questions

What is the corrected calcium formula?▼
Corrected calcium (mg/dL) = measured total calcium + 0.8 × (4.0 − albumin in g/dL). In SI units the same correction is calcium (mmol/L) + 0.02 × (40 − albumin in g/L). Total calcium falls by about 0.8 mg/dL for every 1 g/dL fall in albumin below 4.0 g/dL.
Why does low albumin lower the total calcium?▼
A large part of serum calcium is bound to albumin. When albumin is low, less calcium is bound and total calcium falls, while the ionised (active) calcium can stay normal. A low total calcium that corrects to normal is called pseudohypocalcaemia.
Is this the Payne formula?▼
It is the widely used simplification. Payne and colleagues' 1973 BMJ paper derived adjusted calcium = calcium − albumin + 4.0 (calcium in mg/100 mL, albumin in g/100 mL), which uses a factor of 1.0. The 0.8 factor quoted in most textbooks is smaller; in SI units the two versions appear as 0.020 and 0.025 × (40 − albumin g/L). This tool shows both.
When should you measure ionised calcium instead?▼
Whenever calcium binding is likely to be abnormal — critical illness, acid–base disturbances, liver disease or other conditions that change protein binding. No correction formula is reliable in these settings; ionised calcium (about 1.16–1.31 mmol/L, or 4.65–5.25 mg/dL) is measured directly.
How accurate is albumin-corrected calcium?▼
Less accurate than it looks. A prospective ICU study found that Payne-corrected calcium labelled most patients with true (ionised) hypocalcaemia as normal. Formulas also depend on the albumin assay (bromocresol green versus bromocresol purple), so laboratories are encouraged to derive their own.
How do you convert calcium between mg/dL and mmol/L?▼
Divide mg/dL by 4.008 to get mmol/L, or multiply mmol/L by 4.008 to get mg/dL (calcium's atomic mass is 40.08). For albumin, g/L = g/dL × 10.
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