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Clinical calculator
Albumin-corrected calcium calculator
Adjusts total serum calcium for a low serum albumin. Shows the common 0.8 form and Payne's original 1973 equation.
Albumin-corrected calcium
When this estimate is not valid
- Corrected calcium is an approximation and often disagrees with measured ionised calcium. Measure ionised calcium when the decision matters.
- Kidney failure: correction formulas tend to overestimate calcium.
- Critical illness, acid-base disturbances or albumin below about 3 g/dL: accuracy falls further.
- The 0.8 factor and the 4.0 g/dL reference assume typical assays; some laboratories publish their own adjustment.
Estimate only. Interpret it with the patient's clinical picture and the product label.
How it is calculated
Corrected Ca (mg/dL) = Ca + 0.8 × (4.0 − albumin)
With calcium in mg/dL and albumin in g/dL:
Corrected Ca (mmol/L) = Ca + 0.02 × (40 − albumin)
With calcium in mmol/L and albumin in g/L, this SI form is used as written; it differs from the converted 0.8 form by about 0.2%.
Ca − albumin + 4.0
Payne and colleagues (1973) published the adjustment with a factor of 1.0 (mg/dL and g/dL). The 0.8 factor is a later refinement used by most calculators; the 1973 result is shown as a second line.
With an albumin of 4.0 g/dL or more the value is still calculated, but the correction is normally used only when albumin is low.
Limits: calcium 4–20 mg/dL (about 1.0–5.0 mmol/L), albumin 1–6 g/dL (10–60 g/L).
Worked example
Total calcium 8.0 mg/dL and albumin 2.0 g/dL (0.8 form, then Payne's 1973 equation):
8 + 0.8 × (4.0 − 2) = 9.6 mg/dL8 − 2 + 4.0 = 10.0 mg/dL
Corrected calcium 9.6 mg/dL; 10.0 mg/dL with the 1973 equation.
Questions
Why 0.8 and not 1.0?
Payne's 1973 equation used a factor of 1.0. The 0.8 factor is a later refinement and the form most calculators and references use, so it is the headline here; the 1973 result is shown underneath so you can compare.
How accurate is corrected calcium?
It often disagrees with measured ionised calcium. It is less accurate in kidney failure, where it tends to overestimate calcium, in critical illness, with acid-base disturbances and when albumin is below about 3 g/dL. When the decision matters, measure ionised calcium.
Can I use mmol/L and g/L?
Yes. With calcium in mmol/L the SI form Ca + 0.02 × (40 − albumin g/L) is used; the result is also shown in the other unit (1 mmol/L = 4.008 mg/dL).
Should I correct calcium when albumin is normal?
The correction is normally applied only when albumin is low. With an albumin of 4.0 g/dL or more the calculator still shows the value, with a note.
References
- Payne RB, Little AJ, Williams RB, Milner JR. Interpretation of serum calcium in patients with abnormal serum proteins. Br Med J. 1973;4(5893):643–646. DOI 10.1136/bmj.4.5893.643 PubMed 4758544
- Kenny CM, Murphy CE, Boyce DS, Ashley DM, Jahanmir J. Things We Do for No Reason: calculating a "corrected calcium" level. J Hosp Med. 2021;16(8):499–501. Later adaptation DOI 10.12788/jhm.3619 PubMed 34197298
Formula version: Albumin-adjusted calcium (0.8 factor; Payne 1973 basis) · MediHelp calc v1.0.1
Formula and sources checked on 2026-10-29
