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Estimates sodium deficit for hyponatremia correction planning. Helps determine the total amount of sodium needed to raise serum sodium to a target level.
Clinical decision-support tool for qualified healthcare professionals. Results are not a diagnosis and should not replace professional clinical judgment.
This calculator estimates total body sodium deficit using the Adrogué–Madias formula: deficit = 0.6 × body weight (kg) × (target Na⁺ − current Na⁺). The 0.6 factor approximates total body water as a fraction of body weight and assumes a relatively homogeneous distribution of sodium deficit throughout body water compartments. The calculated value represents a theoretical estimate of sodium deficit at the time of calculation, not a prescription for the amount or rate of sodium replacement. Actual correction depends on the cause of hyponatremia (hypovolemic, euvolemic, hypervolemic), symptom severity, chronicity of the sodium derangement, volume status, choice of replacement fluid, rate of correction strategy, and ongoing monitoring. The deficit must be distributed over time with attention to avoiding overly rapid correction, which carries a risk of osmotic demyelination syndrome. Critical limitations: The formula uses a fixed distribution factor that does not account for age, sex, body composition, or the underlying pathophysiology. It does not estimate ongoing sodium losses, gastrointestinal or urinary. It should not be used to set a rigid replacement target. In acute symptomatic hyponatremia, treatment decisions must be guided by clinical urgency and specialist input, not by a calculated deficit alone. This tool is intended for clinical planning support, not as a replacement for individualized management.
Specialty
Internal MedicineCategory
Internal MedicineDifficulty
Basic
Estimated Time
30 seconds
Version
1.0
Last Updated
2026-08-06
Formula
Keywords
Normal Range
0 mmol
| Classification | Range |
|---|---|
Deficit below normal range | <-100 |
Normal (no deficit) | -100–0 |
Sodium deficit present | ≥0 |
Large sodium deficit | ≥500 |
Estimates the total sodium deficit to guide hyponatremia correction, helping clinicians plan replacement while avoiding over-correction.
Sodium deficit = total body water x (desired sodium - current sodium), where total body water is estimated as 0.6 x weight (kg). Negative values are reported as zero.
Body weight in kilograms; total body water is estimated as 0.6 x weight.
Measured serum sodium in mmol/L, subtracted from the desired sodium.
Target serum sodium in mmol/L, the minuend in the sodium difference.
The sodium deficit is calculated as 0.6 × weight × (target Na − current Na) using an estimated total body water of 0.6 × weight. Values are interpreted against the clinical urgency of correction rather than a fixed normal range.
Estimating the sodium deficit helps clinicians replace sodium methodically and avoid osmotic demyelination syndrome caused by over-rapid correction.
A 70 kg man with chronic hyponatremia has a serum sodium of 125 mmol/L; the goal is 135 mmol/L.
Inputs:
Expected Result: Sodium deficit = 0.6 × 70 × (135 − 125) = 420 mmol. Correct slowly, limiting the rise to 8–10 mmol/L in the first 24 hours.
For chronic hyponatremia, limit correction to 8–10 mmol/L in the first 24 hours and 18 mmol/L in 48 hours to reduce the risk of osmotic demyelination syndrome.
Total body water is approximately 60% of body weight in men and 50% in women. This calculator uses 0.6 × weight as a default estimate.
Estimating water replacement in hypernatremia.
Addresses hypernatremia, not hyponatremia.
Disclaimer: This calculator is intended for educational and clinical decision support purposes only. Sodium correction must be guided by frequent monitoring and institutional protocols.