PUBLIC LIBRARY / CALCULATOR

Free water deficit

Calculates a theoretical deficit using an explicitly selected body-water fraction. The result does not determine replacement, rate or an individual correction target.

Calculate with transparency

Check the population, units and version. The result shows the formula or classification; it does not make an automatic treatment decision.

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Method · Limits of application

Adrogué–Madias 2000; static estimate in adults

This is not a volume to prescribe. Does not model intravascular volume, duration of the abnormality, losses or monitoring. This deficit expression does not apply when Na < 140.

Conditions of use

Check the conditions of application before calculating. The result presents the documented formula or criteria; it does not establish a diagnosis or prescription.

Scope of this implementation

This is not a volume to prescribe. Does not model intravascular volume, duration of the abnormality, losses or monitoring. This deficit expression does not apply when Na < 140.

Parameters in this edition

Sodium · mEq/L
Weight · kg
Estimated total body water fraction
Age · years

Sources and documentation

Method version

Adrogué–Madias 2000; static estimate in adults

Formula and criteria

Estimated deficit = total body water × (Na/140 − 1); total body water = weight × entered fraction.

Population and limitations

This is not a volume to prescribe. Does not model intravascular volume, duration of the abnormality, losses or monitoring. This deficit expression does not apply when Na < 140.

Synthetic cases checked (4)

Synthetic cases for checking the implementation, with no patient data.

Case 1

reference-001

Inputs

Sodium: 155 mEq/L
Weight: 70 kg
Estimated total body water fraction: 0.60
Age: 50 years

{
  "na": 155,
  "peso": 70,
  "grupo": "0.6",
  "idade": 50
}

Expected result

{
  "fwd": 4.5,
  "tbw": 42
}

Actual result

{
  "fwd": 4.500000000000003,
  "tbw": 42
}

Case 2

reference-002

Inputs

Sodium: 165 mEq/L
Weight: 70 kg
Estimated total body water fraction: 0.60
Age: 50 years

{
  "na": 165,
  "peso": 70,
  "grupo": "0.6",
  "idade": 50
}

Expected result

{
  "fwd": 7.5,
  "tbw": 42
}

Actual result

{
  "fwd": 7.500000000000002,
  "tbw": 42
}

Case 3

reference-003

Inputs

Sodium: 140 mEq/L
Weight: 70 kg
Estimated total body water fraction: 0.60
Age: 50 years

{
  "na": 140,
  "peso": 70,
  "grupo": "0.6",
  "idade": 50
}

Expected result

{
  "fwd": 0,
  "tbw": 42
}

Actual result

{
  "fwd": 0,
  "tbw": 42
}

Case 4

reference-004

Inputs

Sodium: 154 mEq/L
Weight: 60 kg
Estimated total body water fraction: 0.45
Age: 50 years

{
  "na": 154,
  "peso": 60,
  "grupo": "0.45",
  "idade": 50
}

Expected result

{
  "fwd": 2.7,
  "tbw": 27
}

Actual result

{
  "fwd": 2.7000000000000024,
  "tbw": 27
}

Source for the active edition

University of Pittsburgh · Water replacement · deficit example and expression

Additional reading and history

Adrogué HJ, Madias NE. Hypernatremia. N Engl J Med, 2000.

Identifier: deficit-de-agua-livre

Original clinical content: Brazilian Portuguese.

Code and reproducibility

This tool’s code on GitHub

Download code and tests

Sources, version and reproduction instructions

README

Local installation

Code license: Apache-2.0

Guidelines and conditions

This repository’s license applies to the code. Third-party instruments, questionnaires, data and models remain subject to their owners’ conditions.

The code tests are technical checks. Clinical approval and professional translation review are recorded separately.

Relationship with cancer research

General context — relationship to be defined

A resource for general clinical contexts. This edition does not assign a specific oncological relationship; selecting it for a study requires a justified question, population and purpose.