Live calculator
Free water deficit calculator
Calculate a transparent free-water-deficit estimate for a selected elevated sodium target. This page is arithmetic support only, not a correction plan.
Safety checks
- Arithmetic only; do not use this page to select fluid, correction time/rate, monitoring interval, or treatment.
- AAHA's 0.6 L/kg total-body-water assumption may not represent every patient or ongoing-loss context.
- Verify the current fluid and electrolyte plan against current references and clinical judgment.
Basis and limits
- Formula: Free Water Deficit (L) = [(current Na / desired Na) − 1] × (0.6 × weight in kg).
- Total-body-water assumption: 0.6 L/kg from AAHA hypernatremia guidance.
- Scope: Estimates deficit arithmetic only. It does not replace clinical judgment or create a correction plan.
Formula
Free water deficit (L): [(current Na / desired Na) − 1] × (0.6 × weight in kg)
Deficit in mL: deficit (L) × 1,000
Last reviewed: May 2026
References: Plumb's Veterinary Drug Handbook, Merck Veterinary Manual, BSAVA Formulary, AAHA Guidelines. Verify against current references before clinical use.