Corrected Calcium Calculator
Adjust a serum calcium result for a low albumin. Because much of the calcium in blood is bound to albumin, a low albumin lowers the total calcium without changing the physiologically active (ionised) fraction. Enter your calcium and albumin in conventional (US) or SI units.
The correction formula
Conventional: corrected Ca (mg/dL) = measured Ca + 0.8 × (4.0 − albumin[g/dL]). SI: corrected Ca (mmol/L) = measured Ca + 0.02 × (40 − albumin[g/L]). Normal albumin is taken as 4.0 g/dL (40 g/L). Source: Payne RB et al., Br Med J 1973.
Frequently asked questions
What is the corrected calcium formula?
In conventional units: corrected calcium (mg/dL) = measured calcium + 0.8 × (4.0 − albumin in g/dL). In SI units: corrected calcium (mmol/L) = measured calcium + 0.02 × (40 − albumin in g/L). For example, a calcium of 8.0 mg/dL with an albumin of 2.0 g/dL corrects to 9.6 mg/dL.
Why does calcium need correcting for albumin?
About 40% of blood calcium is bound to albumin. Total calcium — the number most labs report — therefore falls when albumin is low, even though the active ionised calcium may be normal. The correction estimates what the total calcium would be at a normal albumin of 4.0 g/dL (40 g/L).
What is a normal corrected calcium?
A normal total (or corrected) calcium is roughly 8.5–10.2 mg/dL (2.12–2.55 mmol/L), though the exact interval depends on your laboratory. A corrected result above or below that range should be interpreted by a clinician. This calculator compares your corrected value with that interval and labels it as below, within or above the usual range. Note that the correction only changes anything when albumin is away from 4.0 g/dL (40 g/L) — at a normal albumin the corrected and measured values are identical.
How reliable is the correction?
The albumin correction is a rough adjustment and can be inaccurate — particularly in critical illness, kidney disease and acid–base disturbances. When precise assessment matters, a directly measured ionised calcium is preferred over any correction formula. The formula assumes a fixed relationship between albumin and calcium binding, and that assumption breaks down when pH, other binding proteins or free fatty acids are abnormal. Treat a corrected value that lands close to a decision threshold as provisional and confirm it before acting on it.
Which unit system should I use?
Use the one on your report. Conventional (US) labs report calcium in mg/dL and albumin in g/dL; SI labs use mmol/L and g/L. Switch the toggle to match, and the calculator applies the corresponding formula.
This is a reference tool, not a diagnosis or medical advice. Results depend on the laboratory, assay and clinical context, and reference intervals vary between labs and by age and sex — always read your result against the range printed on your own report and discuss it with a qualified healthcare professional.
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