Anion Gap Calculator

Work out anion gap instantly with clear inputs, formula shown and shareable results.

About Anion Gap Calculator

Subtracts chloride and bicarbonate from sodium to give the anion gap, then corrects it for albumin, which carries most of the unmeasured anion charge.

Formula

Anion gap

AG = Na - (Cl + HCO3); albumin-corrected AG = AG + 2.5 x (4 - albumin g/dL)

Worked example

With the default values below, Anion Gap Calculator returns Anion gap of 12.0. Change any input above and every figure here is recalculated in your browser.

Inputs used

Sodiumaccepts 100–180 mmol/L: 140 mmol/L
Chlorideaccepts 70–140 mmol/L: 104 mmol/L
Bicarbonateaccepts 2–50 mmol/L: 24 mmol/L
Albuminaccepts 1–6 g/dL: 4 g/dL

Results

Anion gap: 12.0 mmol/L
Albumin-corrected anion gap: 12.0 mmol/L
Interpretation: Normal anion gap (8-12 mmol/L)

Step by step

1Values used
2Anion gap
3Anion gap= 12.0 mmol/L
4Albumin-corrected anion gap= 12.0 mmol/L
5Interpretation= Normal anion gap (8-12 mmol/L)

Assumptions and limits

The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
Figures are rounded for display to 1 decimal place, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
Educational estimate only. Not a substitute for professional clinical judgement, and must not be used to make treatment or dosing decisions.
This is an estimate for general information and not professional medical advice. See the full disclaimer for the limits that apply to this kind of calculator.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Educational estimate only. Not a substitute for professional clinical judgement, and must not be used to make treatment or dosing decisions.

Frequently Asked Questions

Should potassium be included?

Some laboratories add potassium, which raises the reference range by about 4 mmol/L; the common form omits it.

Why correct for albumin?

Albumin is the largest unmeasured anion, so hypoalbuminaemia masks a genuinely raised gap.