Free Water Deficit
Estimated water deficit in hypernatremia.
What is Free Water Deficit?
Estimated water deficit in hypernatremia. Free Water Deficit is intended for use in: Adults.
How to Use the Free Water Deficit Calculator
- Enter Weight in kg.
- Enter Sex.
- Enter Current sodium in mEq/L.
- Enter Target sodium in mEq/L. Defaults to 140 mEq/L if left blank
- Click Calculate to see your result and interpretation.
Formula & Version
This calculator uses formula version 1.0, last reviewed September 2026.
Clinical Considerations & Limitations
- Guideline-recommended correction is typically no faster than ≈10-12 mEq/L per 24 hours in chronic hypernatremia to reduce cerebral edema risk — this tool gives the total deficit only, not a safe hourly rate.
- Uses standard adult total-body-water fractions; less accurate in children, the elderly, or edematous states.
References
- Standard formula: Free Water Deficit = TBW × ((Na measured / Na target) − 1)
Frequently Asked Questions
What is Free Water Deficit?
Estimated water deficit in hypernatremia.
Who is Free Water Deficit intended for?
Adults. Always confirm applicability to your specific patient before use.
What are the limitations of Free Water Deficit?
Guideline-recommended correction is typically no faster than ≈10-12 mEq/L per 24 hours in chronic hypernatremia to reduce cerebral edema risk — this tool gives the total deficit only, not a safe hourly rate. Uses standard adult total-body-water fractions; less accurate in children, the elderly, or edematous states.
What formula or reference does Free Water Deficit use?
Standard formula: Free Water Deficit = TBW × ((Na measured / Na target) − 1)
Is Free Water Deficit a diagnosis?
No. Free Water Deficit produces a score or estimate to support clinical decision-making — it is not a diagnosis and should be interpreted alongside full clinical judgement.
