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Free Water Deficit Calculator

Litres of free water needed to correct hypernatremia.

Compute the free-water deficit in litres for a hypernatremic patient, using the Adrogué-Madias formulation: deficit = TBW × (current Na / target Na − 1).

Priya Venkatesan By Priya Venkatesan
Reviewed by Dr. Helena Ortiz
Published Last reviewed 1 min read

Inputs

kg
mEq/L
mEq/L

Results

Enter values and click Calculate to see results.
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How to use this calculator

  1. Fill in the inputs above using the units you already have.
  2. Values update automatically as you type — no submit button needed.
  3. Hover any result row for the underlying formula and intermediate values.

Formula

TBW = body weight × factor (0.6 men, 0.5 women, 0.5/0.45 elderly). Deficit = TBW × (Na_current / Na_target − 1).

In depth

Compute the free-water deficit in litres for a hypernatremic patient, using the Adrogué-Madias formulation: deficit = TBW × (current Na / target Na − 1).