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Sodium Deficit Calculator

Work out sodium deficit instantly with clear inputs, formula shown and shareable results.

About Sodium Deficit Calculator

Multiplies total body water by the gap between target and current sodium to give the millimoles of sodium required, then converts that to a volume of 3% saline.

Formula

Sodium deficit

Deficit (mmol) = total body water (L) x (target Na - current Na); 3% saline contains 513 mmol/L of sodium

Worked example

With the default values below, Sodium Deficit Calculator returns Sodium deficit of 420.0. Change any input above and every figure here is recalculated in your browser.

Inputs used

Body weightaccepts 2–250 kg
70 kg
Current sodiumaccepts 90–160 mmol/L
125 mmol/L
Target sodiumaccepts 100–150 mmol/L
135 mmol/L
Total body water factorone of Adult male 0.6, Adult female 0.5, Elderly male 0.5, Elderly female 0.45
Adult male 0.6

Results

Sodium deficit
420.0 mmol
Total body water
42.0 L
Equivalent volume of 3% saline
819 mL

Step by step

  1. 1Values used
  2. 2Sodium deficit
  3. 3Sodium deficit= 420.0 mmol
  4. 4Total body water= 42.0 L
  5. 5Equivalent volume of 3% saline= 819 mL

Assumptions and limits

  • The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
  • In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
  • Figures are rounded for display to 1 decimal place, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
  • Educational estimate only. Not a substitute for professional clinical judgement, and must not be used to make treatment or dosing decisions.
  • This is an estimate for general information and not professional medical advice. See the full disclaimer for the limits that apply to this kind of calculator.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Educational estimate only. Not a substitute for professional clinical judgement, and must not be used to make treatment or dosing decisions.

Frequently Asked Questions

How fast should sodium be corrected?

Chronic hyponatraemia is usually corrected by no more than 8 to 10 mmol/L in 24 hours to avoid osmotic demyelination.

Why does the water factor change with age?

Lean body water falls with age and is lower in women, so the same weight holds less total body water.

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