Use our Free Water Deficit Calculator to estimate the amount of free water a patient needs to restore normal serum sodium levels. This tool is helpful for healthcare professionals managing hypernatremia in adults, children, or pediatric patients, providing quick, evidence-based calculations based on patient weight, sodium levels, and sex.
Free Water Deficit (FWD) refers to the amount of water the body is missing due to elevated serum sodium concentrations, most commonly seen in hypernatremia. This calculator helps estimate the volume of hypotonic fluid required to correct that imbalance and safely normalize sodium levels.
This tool utilizes standard clinical formulas to assist medical professionals in determining the required fluid replacement.
FWD (L) = TBW × [(Na_measured / Na_desired) – 1]
Male: 0.6 (adult), 0.6–0.7 (child)
Female: 0.5 (adult), 0.5–0.6 (child)
Example: For a 65kg adult female with Na⁺ = 150 mEq/L and target Na⁺ = 140:
TBW = 65 × 0.5 = 32.5
FWD = 32.5 × [(150 / 140) – 1] = 2.32 L
This is the volume of water required to lower sodium safely.
This tool is designed for clinicians managing:
Important: Always use clinical judgment to determine the rate of correction — overly rapid correction may result in cerebral edema, especially in children.
Free water deficit refers to the volume of water that must be replaced to correct high serum sodium levels (hypernatremia) and restore fluid balance.
It’s calculated using total body water (TBW) and the ratio between measured and desired sodium:
FWD = TBW × [(Na_measured / Na_desired) – 1].
Yes, it includes options for pediatric patients, but always verify total body water percentages appropriate for the child’s age and consult pediatric guidelines.
Generally, serum sodium should not decrease more than 10–12 mEq/L in 24 hours. Slower correction is safer, especially in chronic cases.
Yes, it’s frequently used in DKA and critical care scenarios. However, always consider comorbidities and fluid balance holistically.
This site provides general information for educational purposes only and does not constitute financial, legal, medical, or professional advice. calckits.com makes no warranties as to the accuracy or reliability of results. Always consult with a qualified professional for personalized guidance.