Corrected Calcium Calculator
Adjust serum calcium for albumin level using the Payne correction formula. Low albumin causes falsely low measured total calcium values.
Results
What is it?
Approximately 40–45% of serum calcium is bound to albumin. When albumin is low, total calcium is falsely low even if ionised (free) calcium is normal. Payne's correction formula adjusts for this: Corrected Ca (mmol/L) = Measured Ca + 0.02 × (40 − Albumin g/L). Normal corrected calcium is 2.20–2.60 mmol/L (8.8–10.4 mg/dL).
How to use
Enter the measured total serum calcium and the serum albumin from the same blood sample. Select the unit system. The normal albumin reference point is conventionally 40 g/L (SI) or 4.0 g/dL (US).
Example scenario
Patient: Ca = 1.95 mmol/L, Albumin = 25 g/L. Corrected Ca = 1.95 + 0.02 × (40 − 25) = 1.95 + 0.30 = 2.25 mmol/L. The measured 1.95 appears hypocalcaemic, but the corrected value of 2.25 is within normal range — no true hypocalcaemia.
Pro tip
Corrected calcium should only be used as a screening tool. For definitive assessment of calcium status (especially in critically ill patients, acid-base disturbances, or hyperproteinaemia), measure ionised calcium directly. Always interpret corrected values alongside clinical symptoms.