Bicarbonate Deficit Calculator
Estimate the bicarbonate needed to correct acidosis.
Result
How it is calculated
The estimate is deficit = 0.5 × W × (target − measured), where W is body weight in kg and both bicarbonate values are serum HCO₃ in mEq/L. The 0.5 factor is the assumed bicarbonate distribution space (half of body weight), and the target is whatever value you type, not a fixed 24. The result is the total bicarbonate in mEq needed to lift the measured value to that target, rounded to a whole mEq. The tool shows no result when the weight is outside 2–650 kg, the measured value is negative, the target is above 60, or the target is not higher than the measured value, since a deficit only exists when the target is above the current level. It is a single-formula estimate and does not model how the distribution space changes in severe acidosis.
Worked example
A patient weighs 70 kg with a measured HCO₃ of 10 mEq/L and a target of 24 mEq/L. The gap is 24 − 10 = 14 mEq/L. Half of body weight is 0.5 × 70 = 35 L of distribution space. Multiplying: 35 × 14 = 490. The calculator shows 490 mEq.
Common mistakes
- Entering the target lower than or equal to the measured value (for example a target of 24 with a measured value of 26). There is no deficit in that case and the tool returns nothing.
- Typing weight in pounds. The formula expects kilograms, and a weight under 2 or over 650 gives no result, but 154 lb typed as 154 is accepted and overstates the deficit by more than double.
- Entering the anion gap, base excess or blood pH in the HCO₃ field. Only the serum bicarbonate concentration in mEq/L belongs there; a target above 60 or a negative measured value is rejected.
- Treating the figure as a dose. It is the size of the gap in total mEq, not an amount to give at once.
About this calculator
The bicarbonate deficit is a bedside estimate used in metabolic acidosis, calculated here as 0.5 × body weight (kg) × (target HCO₃⁻ − measured HCO₃⁻), where 0.5 approximates the bicarbonate space (roughly 40–50% of body weight, with the larger fraction used in more severe acidosis) that the ion distributes into, and the target is the serum bicarbonate you want to reach — often around 24 mEq/L, the typical normal value. The result is the estimated total mEq of bicarbonate needed to close the gap between the patient's current HCO₃⁻ and that target.
This calculation is used in emergency medicine and critical care when evaluating patients with severe metabolic acidosis — from diabetic ketoacidosis, renal tubular acidosis, severe diarrhea, or lactic acidosis — to estimate the scale of the bicarbonate gap before any correction is considered. Nephrologists and intensivists use the same kind of formula (with 0.4 as the weight factor in some references) when assessing chronic kidney disease patients with persistently low bicarbonate.
This calculator takes body weight, the patient's measured HCO₃⁻ and your chosen target HCO₃⁻ (which must be higher than the measured value) and returns the estimated deficit in mEq, giving clinicians a starting reference figure for how large the underlying acid-base disturbance is.
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