About the Corrected Calcium Calculator
About 40% of the calcium in blood is bound to albumin. When albumin is low — common in hospital patients, liver disease, kidney disease and malnutrition — total calcium falls even though the active, ionised calcium may be perfectly normal. The corrected (or adjusted) calcium estimates what the total calcium would be if albumin were normal, so it can be compared with the usual reference range.
Enter total serum calcium and albumin in US units (mg/dL and g/dL) or SI units (mmol/L and g/L). The calculator applies the Payne correction, shows the result in both unit systems and flags whether it is below, within or above the typical 8.5–10.5 mg/dL (2.12–2.62 mmol/L) range.
Corrected calcium is a convenient estimate but can be misleading in critical illness, severe kidney disease and acid–base disturbances. When accuracy matters, a directly measured ionised calcium is preferred. This tool is for education and clinical support, not diagnosis.
With the default inputs, the corrected calcium is 9.2. Change any value above to recalculate instantly.
How to use the corrected calcium calculator
- 1Choose US (mg/dL) or SI (mmol/L) units to match your lab report.
- 2Enter the total serum calcium.
- 3Enter the serum albumin.
- 4Read the corrected calcium and its interpretation.
Formula and method
The Payne formula assumes that each 1 g/dL fall in albumin below a reference of 4.0 g/dL lowers total calcium by about 0.8 mg/dL. The SI version is the same relationship expressed in mmol/L and g/L: 0.02 mmol/L of calcium per 1 g/L of albumin below 40 g/L.
Results are converted between units with 1 mmol/L = 4.008 mg/dL (the molar mass of calcium is 40.08 g/mol). The reference range used for interpretation is 8.5–10.5 mg/dL (about 2.12–2.62 mmol/L); individual laboratories may quote slightly different ranges.
- Ca
- Measured total serum calcium
- albumin
- Serum albumin (g/dL or g/L)
- Ca_corr
- Albumin-corrected calcium
Worked examples
Low albumin masking a normal calcium
Measured calcium of 8.0 mg/dL looks low, but albumin is 2.5 g/dL. The correction is 0.8 × (4.0 − 2.5) = 1.2, giving a corrected calcium of 9.2 mg/dL (2.30 mmol/L) — within the normal range.
Hidden hypercalcaemia
A calcium of 10.2 mg/dL is near the top of normal, but with albumin at 3.0 g/dL the corrected value is 10.2 + 0.8 = 11.0 mg/dL, which is above the 10.5 mg/dL upper limit.
SI units: 2.00 mmol/L with albumin 25 g/L
Albumin is 15 g/L below 40, so 0.02 × 15 = 0.30 mmol/L is added. The corrected calcium is 2.30 mmol/L, or about 9.22 mg/dL.
Frequently asked questions
Why does calcium need to be corrected for albumin?+
About 40% of blood calcium is bound to albumin. When albumin is low, total calcium falls even if the physiologically active ionised calcium is normal, so correction helps avoid a false diagnosis of low calcium.
What is a normal corrected calcium?+
A typical adult reference range is about 8.5–10.5 mg/dL, or 2.12–2.62 mmol/L. Laboratories vary slightly, so compare with the range printed on the report.
Should I correct calcium when albumin is normal or high?+
Many clinicians only correct when albumin is low. Applying the formula with a high albumin subtracts calcium; the result is still an estimate, and ionised calcium is the definitive test.
When is corrected calcium unreliable?+
The formula performs poorly in critical illness, advanced chronic kidney disease, very low albumin and acid–base disorders. In these situations a measured ionised calcium is recommended.
How do I convert calcium from mg/dL to 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, 10 mg/dL equals about 2.50 mmol/L.
This tool gives general estimates and is not medical advice. Talk to a doctor or qualified professional about your health, diet or training.