Anion gap calculator
The anion gap is a calculation from sodium, chloride and bicarbonate that helps clinicians look into the acid-base balance of your blood. Type your results in the units on your report and it works out Anion Gap as you type, in your browser.
AI-verified against cited sources. Awaiting expert reviewLast reviewed 2026-10-03Electrolytes & Minerals
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Educational information, not medical advice. Blood Test Tracker doesn’t diagnose or treat, and it doesn’t replace your clinician. Talk with your clinician before changing medications, supplements or care.
How it’s worked out
The formula
Anion gap (mmol/L) = Na − (Cl + HCO3), all in mmol/L. Some labs, particularly outside the US, add potassium: (Na + K) − (Cl + HCO3). Albumin-adjusted variant (Figge 1998): adjusted gap = observed gap + 2.5 × (normal albumin − observed albumin), with albumin in g/dL.
A worked example
Example numbers, not anyone’s real results, run through the same code as the calculator above.
| Sodium | 140 mmol/L |
|---|---|
| Chloride | 104 mmol/L |
| Bicarbonate | 24 mmol/L |
| Anion Gap | 12 mmol/L |
For an adult, this result is in the usual range.
What Anion Gap tells you
The anion gap is not measured directly. Your lab calculates it from three electrolytes on a routine panel: sodium minus the sum of chloride and bicarbonate. The result stands for the negatively charged particles in your blood that the panel does not measure, such as albumin, phosphate and organic acids. When acids build up, the gap usually widens. The usual range depends on the lab's instruments, so the range on your own report matters most.
A higher-than-usual gap most often points toward a build-up of acid in the blood (metabolic acidosis), for example from poorly controlled diabetes, kidney problems or certain poisons. A lower-than-usual gap most often reflects a low albumin level or a lab error. The number is only a clue. Normal ranges are wide, so a meaningful rise can still sit inside your lab's range. It is read together with bicarbonate, albumin, kidney function, glucose and your symptoms.
Read the full page on Anion Gap, with what a high or low result can mean.
Usual ranges
The ranges the result above is placed on. Your own lab’s printed range comes first if it gives one.
Sources
The equation
- Serum anion gap: its uses and limitations in clinical medicine, Clinical Journal of the American Society of Nephrology (2007)
- Electrolyte Panel, Serum (test ID ELPSR), Mayo Clinic Laboratories (catalog copy hosted by Schneck Medical Center)
- Acid-Base Disorders, Merck Manual Professional Version
- Anion gap and hypoalbuminemia, Critical Care Medicine (1998)
5 more sources for the ranges and the explanation
- Basic Metabolic Panel, Serum (test ID BMAMA), Mayo Clinic Laboratories (catalog copy hosted by Schneck Medical Center)
- Basic Metabolic Panel (test 0020399), ARUP Laboratories
- The serum anion gap in the evaluation of acid-base disorders: what are its limitations and can its effectiveness be improved?, Clinical Journal of the American Society of Nephrology (2013)
- Metabolic Acidosis, Merck Manual Professional Version (2025)
- Anion Gap Blood Test, MedlinePlus (US National Library of Medicine)
AI-verified against cited sources. Awaiting expert review. Last reviewed 2026-10-03. The calculator is version 1.0.0 of our code for this equation, tested against published examples. How we build and check these pages.