---
title: Anion Gap Calculator (with Albumin Correction)
type: tool
url: "https://www.test-well.com/tools/anion-gap-calculator"
date_published: 2026-09-26
free: true
---

# Anion Gap Calculator (with Albumin Correction)

> Enter sodium, chloride and bicarbonate (reported as CO₂ on a metabolic panel) and the calculator returns the anion gap, Na − (Cl + HCO₃), in mEq/L; add albumin and it also shows the albumin-corrected gap. Modern analyzers put the usual range around 3–11 mEq/L. An elevated gap with a low bicarbonate points to unmeasured acids and needs prompt evaluation.

## Key facts

| Fact | Value |
| --- | --- |
| Inputs | Na · Cl · HCO₃ (· albumin) |
| From | BMP or CMP |
| Usual range | ≈ 3–11 mEq/L (lab-dependent) |
| Cost | Free |

## For agents

See https://www.test-well.com/developers for the agent endpoints.

## Frequently asked questions

### Where is bicarbonate on my lab report?

US metabolic panels report it as 'CO2', 'carbon dioxide' or 'total CO2' in mEq/L or mmol/L (the two are identical for these ions). That value is almost entirely bicarbonate and is what the formula uses.

### Why is the normal anion gap different in different sources?

Because it depends on the analyzer. Older methods measured chloride lower, giving a reference range of roughly 8–16 mEq/L; modern ion-selective electrodes read chloride higher, so the gap is smaller and labs now quote about 3–11. Use the range printed on your own report.

### Why correct for albumin?

Albumin is the largest unmeasured anion. Each 1 g/dL fall in albumin lowers the gap by about 2.5 mEq/L, so a person with low albumin can hide a real acidosis behind a 'normal' gap. Adding 2.5 × (4.0 − albumin) restores it.

### Does this calculator include potassium?

No — it uses the common US convention Na − (Cl + HCO₃). Some references add potassium, which raises every value by about 4 mEq/L and shifts the reference range up by the same amount; do not compare the two conventions directly.

## Related

- [sodium](https://www.test-well.com/biomarkers/sodium)
- [chloride](https://www.test-well.com/biomarkers/chloride)
- [carbon dioxide](https://www.test-well.com/biomarkers/carbon-dioxide)
- [albumin](https://www.test-well.com/biomarkers/albumin)
- [potassium](https://www.test-well.com/biomarkers/potassium)
- [comprehensive metabolic panel](https://www.test-well.com/tests/comprehensive-metabolic-panel)
- [basic metabolic panel](https://www.test-well.com/tests/basic-metabolic-panel)
- [electrolyte panel](https://www.test-well.com/tests/electrolyte-panel)

---

Canonical page: https://www.test-well.com/tools/anion-gap-calculator
Machine-readable catalog: https://www.test-well.com/api/catalog.json · MCP server: https://www.test-well.com/mcp · Overview for agents: https://www.test-well.com/llms.txt

Prices are cash-pay, in USD, and include physician authorization; every order adds one flat $6 lab processing fee. Educational content is not a diagnosis — discuss results with a clinician.