Last updated October 12, 2026 · Report an error
Anion Gap (AG) = Sodium - (Chloride + Bicarbonate), the standard published formula used to help classify metabolic acidosis. Optionally includes potassium (AG = (Na + K) - (Cl + HCO3)), a commonly cited variant. Commonly cited reference ranges are roughly 8-16 mEq/L (without potassium) or 10-20 mEq/L (with potassium); exact ranges vary by lab assay. Pure arithmetic on given lab values. For general reference and educational purposes only — not a medical diagnosis. Consult a doctor for actual electrolyte and acid-base assessment.
How it works
Enter sodium, chloride, and bicarbonate. Optionally include potassium for the alternative formula. The tool applies the anion gap formula and compares the result to the standard reference range.
- Enter sodium, Na (mEq/L).
- Enter chloride, Cl (mEq/L).
- Enter bicarbonate, HCO3 (mEq/L).
- Enter include potassium in the formula?.
- Enter potassium, K (mEq/L) — only if included above.
- Click Calculate to see your results.
Examples
Na 140, Cl 100, HCO3 24
AG = 140 - (100 + 24) = 16 mEq/L — at the upper edge of the commonly cited 8-16 mEq/L normal range.
Who should use it
- Reviewing a basic metabolic panel result.
- Nephrology, emergency medicine, and critical care education about acid-base disorders.
Industry applications
- Emergency medicine and critical care reference
- Nephrology education
Advantages
- Simple, standard, widely taught formula.
- Supports both common variants (with and without potassium).
Limitations
- Reference ranges vary somewhat by lab assay.
- Can be affected by serum albumin level, which this basic formula does not adjust for.
Common mistakes to avoid
- Comparing a potassium-inclusive AG against the Na-only reference range (or vice versa).
- Not accounting for albumin — a low albumin level can lower the expected normal anion gap, per commonly cited nephrology teaching.
Best practices
- If serum albumin is low, discuss with your doctor about an albumin-corrected anion gap for a more accurate assessment.
Tips
- The anion gap is typically interpreted alongside bicarbonate, pH, and the clinical picture — not as a standalone number.