Health
BMI, calorie & wellness calculators
Anion Gap Calculator with Potassium
Some laboratories and textbooks include potassium in the anion gap, and this calculator lets you switch to that convention: AG = (Na + K) − (Cl + HCO₃) instead of the more common Na − (Cl + HCO₃). Adding potassium raises the result by roughly the potassium value, so the normal range shifts up too — from the classic 8–12 mmol/L without potassium to about 12–16 mmol/L with it. For a panel of sodium 140, potassium 4, chloride 104 and bicarbonate 24, the with-potassium gap is (140 + 4) − (104 + 24) = 16 mmol/L, the upper end of its normal range, versus 12 mmol/L without. The key point is consistency: use the range that matches the formula you chose, because comparing a with-potassium gap against a without-potassium range would falsely suggest a raised gap. Enter the electrolytes, toggle potassium on, and see the gap with the correct normal range. This is an interpretation aid, not a diagnosis — verify clinically. Free, private, and computed entirely in your browser.
AG = (Na + K) − (Cl + HCO₃) — the with-potassium convention
- Worked example: (140 + 4) − (104 + 24) = 16 mmol/L
- Normal range shifts up to ≈ 12–16 mmol/L when K is included
Frequently asked questions
Should potassium be included in the anion gap?
Both conventions are used. The common form is Na − (Cl + HCO₃) with a normal range of about 8–12 mmol/L; the with-potassium form (Na + K) − (Cl + HCO₃) adds potassium and has a higher normal range of about 12–16 mmol/L. Neither is wrong — the essential thing is to compare the result against the matching range. It is an interpretation aid, not a diagnosis.
How much does potassium change the anion gap?
Including potassium raises the anion gap by roughly the potassium concentration (typically 3.5–5 mmol/L), so a gap of 12 without potassium becomes about 16 with it for a potassium of 4. The normal range shifts up by the same amount, so a with-potassium gap of 16 is still normal. Always read the number against the range for the formula you used.