Sodium Deficit Calculator

Written by Great Medico

Updated September 24, 2026 •2 min read

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When sodium, bicarbonate, osmolality, or an infusion rate is changing, clean arithmetic matters. Sodium Deficit Calculator focuses on the exact variables shown in the tool and returns the estimate its engine supports.

What this calculator does

Sodium Deficit Calculator uses Age / sex category, Weight, Serum sodium, and Desired sodium to calculate sodium deficit. Where supported, it also shows Estimated TBW so the primary result is easier to check. It follows the exact field flow and engine behavior in this plugin rather than describing a different calculator with the same name. Fluid and electrolyte formulas are sensitive to units, timing, ongoing losses, kidney function, and rapidly changing physiology. They are most useful as structured estimates alongside repeat measurements and bedside assessment.

How to use it

Enter or select Age / sex category, Weight, Serum sodium, and Desired sodium. Use the units offered by the calculator and keep paired laboratory or treatment values from the same clinical episode whenever the formula assumes that. If an entry is unknown, do not substitute a guess simply to obtain a number.

How the calculation works

The calculator estimates total body water from body weight and the selected age/sex factor, then multiplies TBW × (desired sodium − measured sodium) to estimate sodium deficit in mmol.

Example

Using the sample values prefilled in this calculator, the primary result is 630 mmol (Sodium deficit) and Estimated TBW is 42 L. This example demonstrates the plugin’s own calculation path; replace the sample inputs with verified values before interpreting a real result.

How to interpret the result

Read the output as sodium deficit from the implemented formula. Compare it with measured values, volume status, ongoing inputs/losses, and serial trends; treatment decisions should not rely on the calculator in isolation.

Limitations and notes

A calculated sodium deficit does not define how much sodium can safely be given or how fast. Chronicity, neurologic symptoms, volume status, potassium, ongoing losses, and correction limits must guide treatment.