Corrected Calcium Calculator
Adjust your serum calcium for your albumin level using the Payne formula.
What is corrected calcium?
About half of the calcium in your blood is bound to a protein called albumin, and the other half is "free" (ionised) and biologically active. A standard calcium test measures the total. When albumin is low - which happens often in illness, malnutrition or liver and kidney disease - the total calcium reads low even though the active calcium may be perfectly normal. Corrected calcium estimates what the total would be if your albumin were normal, so you are not misled.
How this calculator works
It uses Payne's formula: corrected calcium (mg/dL) = measured calcium + 0.8 x (4.0 - albumin in g/dL). In other words, for every 1 g/dL that albumin sits below the reference of 4.0, the calcium is nudged up by 0.8. Use the toggles if your lab reports calcium in mmol/L or albumin in g/L. Everything is calculated in your browser and nothing is stored.
What your result means
| Corrected calcium | Interpretation |
|---|---|
| Below 8.5 mg/dL | Low (hypocalcaemia range) |
| 8.5 to 10.2 mg/dL | Normal |
| Above 10.2 mg/dL | High (hypercalcaemia range) |
Reference ranges vary slightly by lab, so use your report's own range where it differs.
An important caveat
The correction is only an approximation, and studies show it is not always accurate - particularly in kidney disease and critical illness. When your calcium status genuinely matters for a decision, a direct ionised (free) calcium test is the more reliable measurement. Discuss any abnormal result, and the likely cause, with your doctor.
Frequently asked questions
Why correct calcium for albumin?
About half the calcium in your blood travels bound to the protein albumin. When albumin is low (common in illness), the total calcium reading looks low even if the active, free calcium is normal. Correcting adjusts for that.
What is the normal corrected calcium?
Roughly 8.5 to 10.2 mg/dL, though the exact reference range varies slightly between labs.
Is corrected calcium always reliable?
It is an approximation. When calcium status really matters - for example in kidney disease or critical illness - a direct ionised (free) calcium test is more accurate.
What albumin level is normal?
Around 3.5 to 5.0 g/dL. The Payne formula assumes a reference albumin of 4.0 g/dL and adjusts the calcium by 0.8 mg/dL for every 1 g/dL the albumin is away from that.
What causes high or low calcium?
High calcium can come from an overactive parathyroid gland, some cancers or excess vitamin D. Low calcium can come from vitamin D deficiency, kidney disease or low parathyroid activity. Your doctor investigates the cause.
Formula source: Payne RB et al. Interpretation of serum calcium in patients with abnormal serum proteins. BMJ 1973;4:643-646.
Related reading
Want every value on your report explained?
Upload your lab report PDF and get a plain-language explanation of every parameter, in under 2 minutes.
Get started free