What TBW fraction does this calculator use?

Males use 0.6, females 0.5, and elderly patients (≥65) use 0.45 — standard values from Adrogue-Madias and similar references.

What is a safe correction rate?

For chronic hyponatremia (onset >48 h), the rate should not exceed 8–10 mEq/L per 24 hours to avoid osmotic demyelination syndrome. Acute symptomatic cases may tolerate 1–2 mEq/L per hour for the first 3–4 hours.

What target sodium should I use?

A safe initial target is 125–130 mEq/L. The full correction goal is typically 135–145 mEq/L, but overshoot risks osmotic demyelination. Consult clinical guidelines for your patient's specific situation.

Does this account for ongoing losses?

No. This formula estimates the static deficit only. Ongoing urinary or GI sodium losses require additional replacement beyond this estimate.

Is this a substitute for clinical judgment?

No. This tool is for educational and reference use. Treatment decisions must be made by a licensed clinician accounting for the full clinical picture.

Sodium Deficit Calculator

Name: Sodium Deficit Calculator
Availability: InStock
Author: Nham Vu

Enter patient weight, sex, current sodium, and target sodium to calculate the total body sodium deficit and safe correction guidance.

Patient Inputs

Body Weight

Sex

Male Female

Age Group

Current Serum Sodium (mEq/L)

Typical hyponatremia range: 100–134 mEq/L

Target Serum Sodium (mEq/L)

Safe initial target: 125–130 mEq/L

Onset

Results

Fill in the inputs and click Calculate.

Summary

Enter patient weight, sex, current sodium, and target sodium to calculate the total body sodium deficit and safe correction guidance.

How it works

Enter the patient's weight in kilograms (or pounds — select unit).
Select sex and age group to determine the TBW fraction.
Enter the current measured serum sodium (mEq/L).
Enter the target serum sodium (typically 125–135 mEq/L).
The calculator applies: Na deficit = TBW × (target Na − current Na).
Correction rate guidance is shown based on whether the case is acute or chronic.

Use cases

Estimating sodium replacement needs in symptomatic hyponatremia.
Determining approximate volume of saline infusion required.
Teaching clinical pharmacology and fluid/electrolyte physiology.
Cross-checking manual calculations during clinical rounds.
Planning correction strategy for acute vs. chronic hyponatremia.

Frequently Asked Questions

Last updated: 2026-07-01 · Reviewed by Nham Vu