Corrected Calcium Calculator (Payne Formula)

Corrected calcium is total blood calcium adjusted for albumin using the Payne formula, published in 1973. About 40% of calcium in blood is bound to albumin, so when albumin is low, measured total calcium looks falsely low even when the active ionized calcium is normal. Corrected calcium estimates what total calcium would be if albumin were at the normal reference of 4.0 g/dL (40 g/L).

Corrected calcium (mg/dL) = measured calcium (mg/dL) + 0.8 x (4.0 - albumin in g/dL). Worked example: measured calcium 8.0 mg/dL with albumin 3.0 g/dL gives 8.0 + 0.8 x (4.0 - 3.0) = 8.80 mg/dL, which is within the normal range (correction +0.80 mg/dL).

Corrected calcium (mmol/L) = measured calcium (mmol/L) + 0.02 x (40 - albumin in g/L). Worked example: calcium 2.00 mmol/L with albumin 30 g/L gives 2.00 + 0.02 x (40 - 30) = 2.20 mmol/L (correction +0.20 mmol/L).

Divide mg/dL by 4.008 to get mmol/L, or multiply mmol/L by 4.008 to get mg/dL. For example, 2.00 mmol/L equals 8.02 mg/dL. Convert albumin by multiplying g/dL by 10 to get g/L.

The adult reference range for total (and corrected) calcium is 8.5-10.5 mg/dL, which equals 2.12-2.62 mmol/L. Below 8.5 mg/dL (2.12 mmol/L) is hypocalcemia; above 10.5 mg/dL (2.62 mmol/L) is hypercalcemia. Labs vary slightly, so check your own lab's reference range.

This calculator applies the Payne correction only when albumin is below the 4.0 g/dL (40 g/L) reference - the clinically meaningful case, since low albumin falsely lowers measured calcium. When albumin is at or above 4.0 g/dL, it shows 'no correction applied' and the measured value stands.

No. Corrected calcium is an estimate derived from total calcium and albumin. Ionized (free) calcium is the physiologically active form and the gold standard - measured directly with an ion-selective electrode. The normal ionized range is about 1.16-1.32 mmol/L (4.65-5.28 mg/dL). When a result matters clinically, ask for a direct ionized calcium measurement.

Roughly 40% of calcium in blood is bound to albumin and 40-45% circulates as free ionized calcium, with the rest complexed to anions. A drop in albumin removes binding sites, so total calcium falls even though ionized calcium - the part the body actually uses - is unchanged. The 0.8 factor estimates how much calcium (in mg/dL) each gram of albumin carries.

The formula is an estimate, not a measurement. It becomes unreliable with severe acid-base disturbances (pH changes alter albumin binding), paraproteinemia such as myeloma (extra proteins also bind calcium), and extreme critical illness. It was derived from hospitalized patient data in 1973 and assumes a fixed binding ratio that varies between individuals.

No - this calculator is educational only and not medical advice. Calcium disorders can signal serious conditions such as parathyroid disease or malignancy, and treatment decisions require a clinician, full lab context, and usually a direct ionized calcium measurement. If your result is outside the normal range, discuss it with your doctor.