# Corrected Calcium Calculator

> Free albumin-corrected calcium calculator using the Payne 1973 formula. Adjust total serum calcium for low or high albumin. Inputs in mg/dL or mmol/L.

*Source: [https://www.health3.app/tools/corrected-calcium-calculator](https://www.health3.app/tools/corrected-calcium-calculator)*

Adjust your total serum calcium for your albumin level using the Payne 1973 formula. Because roughly 40% of blood calcium is bound to albumin, a low albumin can make total calcium look falsely low. This is an informational reference using a published formula; ionised calcium remains the laboratory gold standard. Supports mg/dL and mmol/L.

 Tracking your calcium and albumin? **See your trends over time** in the Health3 app.

## Why Calcium Is Corrected for Albumin

About 40% of the calcium in your blood travels bound to proteins, mostly albumin, while the rest is free (ionised) or complexed to small anions. A routine "total calcium" test measures all of it. So when albumin is low, common in illness, malnutrition, liver disease, or nephrotic syndrome, the total calcium reads lower even if the biologically active ionised calcium is normal. The albumin correction tries to estimate what the total calcium would be if albumin were normal, so the number is easier to interpret.

The most widely used adjustment is the **Payne formula**, published in 1973 (*British Medical Journal* 4:643–646).

 **Payne formula (1973):**
 `Corrected Ca (mg/dL) = Total Ca + 0.8 × (4.0 − albumin g/dL)`
 SI form: `Corrected Ca (mmol/L) = Total Ca + 0.02 × (40 − albumin g/L)`
 The 4.0 g/dL (40 g/L) constant is the assumed normal albumin.

### Published Reference Range

Adult total (and corrected) calcium reference ranges vary slightly by lab; the band below is a commonly used **published reference range**, not a diagnosis.

| Corrected calcium | mg/dL | mmol/L |
| --- | --- | --- |
| Below reference | Below 8.5 | Below 2.12 |
| Typical reference range | 8.5 – 10.5 | 2.12 – 2.62 |
| Above reference | Above 10.5 | Above 2.62 |

### Important Caveats

- **It is an estimate.** The Payne correction assumes a fixed relationship between albumin and calcium that does not hold in every patient, especially in critical illness or chronic kidney disease.
- **Ionised calcium is the gold standard.** When the true free-calcium status matters clinically, a direct ionised calcium measurement is preferred.
- **pH and other proteins matter.** Acid-base status and other binding proteins also affect free calcium and are not captured by this formula.

### Explore Related Topics

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## Frequently Asked Questions

 What is corrected calcium? Corrected (or adjusted) calcium estimates what your total serum calcium would be if your albumin were normal. About 40% of blood calcium is bound to albumin, so low albumin lowers total calcium even when the active ionised calcium is normal. The most common adjustment is the Payne 1973 formula: corrected Ca (mg/dL) = total Ca + 0.8 x (4.0 - albumin g/dL). When should calcium be corrected for albumin? The correction is most relevant when albumin is abnormal, for example in illness, malnutrition, liver disease, or nephrotic syndrome, where a low albumin can make total calcium look falsely low. When albumin is normal, the correction barely changes the number. It is an estimate, not a replacement for an ionised calcium test. Is corrected calcium accurate? It is an approximation. The Payne formula assumes a fixed albumin-calcium relationship that does not hold in every patient, particularly in critical illness or chronic kidney disease. Some recent studies report that uncorrected total calcium can track ionised calcium as well as the correction does. When precise free-calcium status matters, an ionised calcium measurement is the gold standard. What is a normal corrected calcium level? A commonly used adult reference range for total (and corrected) calcium is about 8.5 to 10.5 mg/dL (2.12 to 2.62 mmol/L), though exact ranges vary by laboratory. These are published reference values, not a diagnosis; interpretation depends on your full clinical picture and should come from your clinician. How do I enter mmol/L values? Switch the unit toggle to mmol/L. Calcium is then entered in mmol/L and albumin in g/L, and the calculator applies the SI form of the Payne formula (corrected Ca = total Ca + 0.02 x (40 - albumin g/L)). The result is shown in mmol/L. **Medical Disclaimer:** Albumin-corrected calcium is an estimate produced by the Payne formula (Payne RB, et al. *Br Med J*. 1973;4(5893):643–646), not a direct measurement. It can be inaccurate in critical illness, chronic kidney disease, and other states; ionised (free) calcium is the laboratory gold standard when precise status is needed. The reference range shown is a general published value, not a diagnosis. This tool is for informational and educational use only. Always consult a qualified healthcare provider to interpret your results.