Free Water Deficit Calculator
Estimate free water deficit with an explicit total-body-water coefficient.
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Estimated free water deficit
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Static estimate; not a direct infusion volume
Estimated free water deficit
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Estimated total body water
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TBW coefficient used: —
About
This calculator estimates a static free water deficit from total body water (TBW), current sodium, and a user-selected target sodium. The TBW coefficient is explicit because one coefficient does not fit every body composition. The estimate is not a direct infusion volume and does not include ongoing losses, intake, urine electrolyte clearance, or redistribution during treatment.
Formula
Interpretation
Units: Sodium may be entered in mmol/L; sodium values in mEq/L are numerically equivalent for this equation. Pounds are converted to kilograms before TBW is estimated.
Worked example: Sodium 160 mmol/L, target 140 mmol/L, 70 kg, and coefficient 0.6 gives TBW 42 L and an estimated deficit of 6 L.
Limitations: This is a snapshot under a constant-total-body-sodium assumption. It does not calculate a correction rate, choose a fluid, or recommend a treatment plan.
FAQ
Disclaimer
Educational and informational reference only. Not intended to replace professional medical advice, diagnosis, treatment, or independent verification.