# Corrected Calcium Calculator

> Adjust total serum calcium for a low or high albumin with the Payne formula, in mg/dL or mmol/L, for use by healthcare professionals.

Category: Healthcare operations · Applies to: Worldwide · Last updated: 2026-10-29
Interactive calculator: https://calculators.geekmidst.com/calculators/corrected-calcium-calculator

The Payne formula adds 0.8 mg/dL of calcium for every 1 g/dL that albumin is below the reference value. It supports, and does not replace, clinical judgement; ionised calcium is the direct measurement.

Also called: Albumin-adjusted calcium calculator.

## Inputs
- Units (options: mg/dL, g/dL, mmol/L, g/L; default conventional)
- Total serum calcium (default 8.0)
- Serum albumin (default 2.0)
- Reference albumin (default 4.0)

## Results
- Corrected calcium (in the units entered)
- Corrected calcium
- Corrected calcium
- Adjustment added

## Formula

```
Corrected Ca (mg/dL) = Measured Ca + 0.8 × (Reference albumin − Measured albumin in g/dL);  mmol/L = mg/dL ÷ 4.0078
```

Where:
- Measured Ca: total serum calcium
- Albumin: serum albumin (g/L ÷ 10 = g/dL)
- 4.0078: mg/dL per mmol/L of calcium (molar mass 40.078 g/mol)

## Worked example
1. Albumin deficit = 4.0 − 2.0 = 2.0 g/dL.
2. Adjustment = 0.8 × 2.0 = 1.6 mg/dL.
3. Corrected calcium = 8.0 + 1.6 = 9.6 mg/dL (9.6 ÷ 4.0078 = 2.40 mmol/L).

**Result:** A total calcium of 8.0 mg/dL with albumin 2.0 g/dL corrects to 9.6 mg/dL (2.40 mmol/L) by the Payne formula.

## What the result means

Compare the corrected value with your laboratory’s reference range for total calcium. When the result would change management, or in critical illness, measure ionised calcium directly instead of relying on the correction.

## Assumptions and limits
- The Payne correction factor of 0.8 mg/dL per g/dL of albumin applies.
- SI values are converted to mg/dL and g/dL, corrected, and converted back.
- The correction is known to be unreliable in critical illness, advanced kidney disease and acid–base disturbance; ionised calcium is preferred there.
- Different laboratories validate different correction equations; use your laboratory’s if it reports one.

## Questions

### What is the SI version of the formula?

It is commonly written as Ca + 0.02 × (40 − albumin in g/L) mmol/L. This calculator converts units exactly instead, and the two agree to about 0.01 mmol/L.

### Is corrected calcium the same as ionised calcium?

No. Corrected calcium estimates what total calcium would be at a normal albumin; ionised calcium is the free, active fraction measured directly.

## Sources
- [WikEM: Corrected calcium (Payne RB et al., BMJ 1973;4:643–646)](https://wikem.org/wiki/Corrected_calcium_calculator)

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_This is a general screening estimate for adults, not medical advice or a diagnosis. Talk to a qualified health professional about your health._

Source: GM¹X CalcVerse — https://calculators.geekmidst.com/calculators/corrected-calcium-calculator