# Anion Gap Calculator

> Calculate the serum anion gap from sodium, chloride and bicarbonate, with the potassium-inclusive gap and the albumin-corrected gap, for healthcare professionals.

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

Anion gap = Na⁺ − (Cl⁻ + HCO₃⁻), in mmol/L. It supports, and does not replace, clinical judgement: interpret it against your own laboratory’s reference range.

Also called: Serum anion gap calculator.

## Inputs
- Sodium (Na⁺) (unit mmol/L; default 140)
- Potassium (K⁺) (unit mmol/L; default 4)
- Chloride (Cl⁻) (unit mmol/L; default 104)
- Bicarbonate (HCO₃⁻) (unit mmol/L; default 24)
- Albumin in (options: g/dL, g/L; default g_dl)
- Serum albumin (default 2.0)
- Reference albumin (default 4.0)

## Results
- Anion gap
- Anion gap including potassium
- Albumin-corrected anion gap

## Formula

```
AG = Na⁺ − (Cl⁻ + HCO₃⁻);  AG with K = (Na⁺ + K⁺) − (Cl⁻ + HCO₃⁻);  Corrected AG = AG + 2.5 × (Reference albumin − Albumin, g/dL)
```

Where:
- Na⁺, K⁺, Cl⁻, HCO₃⁻: serum electrolytes in mmol/L (equal to mEq/L for these ions)
- Albumin: serum albumin; g/L ÷ 10 = g/dL
- 2.5: mmol/L added per 1 g/dL fall in albumin

## Worked example
1. AG = 140 − (104 + 24) = 12 mmol/L.
2. Including potassium: 12 + 4 = 16 mmol/L.
3. Albumin correction: 12 + 2.5 × (4.0 − 2.0) = 17 mmol/L.

**Result:** With Na 140, Cl 104 and HCO₃ 24 the anion gap is 12 mmol/L, which corrects to 17 mmol/L for an albumin of 2.0 g/dL.

## What the result means

Compare the gap with the reference range of the laboratory that ran the test, since ranges depend on the analyser and on whether potassium is included. Low albumin hides a raised gap, which is why the corrected value is shown.

## Assumptions and limits
- All electrolytes come from the same sample and are in mmol/L.
- The albumin correction uses 2.5 mmol/L per g/dL, the commonly quoted factor.
- Reference ranges differ between laboratories; no cut-off is applied here.
- Other unmeasured ions (for example paraproteins, lithium, bromide) can distort the gap.

## Questions

### Should potassium be included?

Most laboratories now leave it out, but some include it. Both values are shown; compare with the range for the method your laboratory uses.

### Why correct for albumin?

Albumin is the main unmeasured anion. When it is low, the gap falls, which can mask an added acid; the correction adds about 2.5 mmol/L per g/dL of missing albumin.

## Sources
- [Wikipedia: Anion gap (formulas, albumin correction, laboratory reference ranges)](https://en.wikipedia.org/wiki/Anion_gap)

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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/anion-gap-calculator