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Free anion gap calculator for basic metabolic panel style electrolytes. Computes the classic gap, an optional potassium-inclusive gap, and a common albumin correction. Use alongside our GFR and creatinine clearance tools on the medical & health hub.
Last updated: April 13, 2026
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Classic anion gap
12 mEq/L
Na⁺ − (Cl⁻ + HCO₃⁻)
Not a substitute for clinical judgment
Reference intervals vary by laboratory and patient context. This tool performs arithmetic only and does not diagnose acid–base disorders.
Reinforce how measured cations and anions relate before adding osmolal gap or delta-delta reasoning.
Verify hand calculations when sodium, chloride, and bicarbonate (or total CO₂ surrogate) are available.
See how a common albumin adjustment changes the gap when serum albumin is low.
Na⁺ = 139, Cl⁻ = 100, HCO₃⁻ = 15 mEq/L → AG ≈ 24 mEq/L.
Interpretation depends on reference range, anion gap elevation, and clinical context—not this page alone.
The calculator subtracts the major measured anions (chloride and bicarbonate) from the major measured cation (sodium) to estimate the balance of unmeasured anions and cations. When you supply potassium, it adds that cation before the same subtraction. When you supply albumin in g/dL, it applies a widely taught linear correction using a 4.0 g/dL reference.
AG = Na⁺ − Cl⁻ − HCO₃⁻AG_K = Na⁺ + K⁺ − Cl⁻ − HCO₃⁻AG_corr = AG + 2.5 × (4.0 − albumin [g/dL])Measured ions leave a residual—the gap—that clinicians interpret with labs, history, and physical exam.
Explore maintenance fluids when resuscitation and electrolyte plans intersect.
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