Anion Gap Calculator

About this calculator

This calculator works out the serum anion gap, a quick lab math check using the formula AG = Na⁺ − (Cl⁻ + HCO₃⁻). It measures the difference between the routinely reported cation and anions in a basic metabolic panel, which normally sits in a narrow reference range.

Clinicians, ER staff, and nursing students use it to classify metabolic acidosis as high-anion-gap (think diabetic ketoacidosis, lactic acidosis, or toxic ingestions) versus normal-anion-gap (like diarrhea or renal tubular acidosis). It's one of the first calculations run when a basic metabolic panel comes back abnormal.