Advanced Fluid Deficit Calculator

Calculator Inputs

Calculation method

Patient type

Current body weight (kg)

Usual or pre-illness weight (kg)

Current weight for comparison (kg)

Estimated dehydration (%)

Serum sodium (mEq/L)

Target sodium (mEq/L)

Expected ongoing losses (mL)

Bolus already given (mL)

Replacement period (hours)

Maintenance method

Adult maintenance rate (mL/kg/day)

Custom maintenance (mL/day)

Temperature for maintenance uplift (°C)

Clinical notes

Example Data Table

Scenario	Method	Weight	Key input	Estimated deficit
Child with gastroenteritis	Clinical dehydration	12 kg	7% dehydration	840 mL
Adult after poor intake	Weight loss	70 kg to 68.8 kg	1.2 kg loss	1200 mL
Older woman with hypernatremia	Free water deficit	60 kg	Na 154, target 140	2700 mL
Infant maintenance review	Pediatric maintenance	8 kg	Holliday-Segar	800 mL/day

Formula Used

Clinical dehydration method: Fluid deficit = body weight in kilograms × dehydration percentage × 10. Each one percent dehydration approximates 10 mL/kg fluid loss.

Weight loss method: Fluid deficit = usual body weight − current body weight, converted to milliliters. A 1 kg acute loss approximates 1000 mL fluid loss.

Free water deficit: Deficit = total body water × ((measured sodium ÷ target sodium) − 1). Total body water is estimated from body weight and patient type.

Pediatric maintenance: Holliday-Segar estimates 100 mL/kg for the first 10 kg, 50 mL/kg for the next 10 kg, and 20 mL/kg above 20 kg.

Temperature uplift: This calculator raises baseline maintenance by 12% for each degree Celsius above 37.8 °C.

How to Use This Calculator

Choose the method that best matches your available data.
Enter the patient type and current body weight.
Add dehydration percent, weight change, or sodium values as needed.
Enter ongoing losses, bolus volume, and the intended replacement period.
Select a maintenance method. Pediatric mode uses Holliday-Segar automatically.
Use adult rate or custom maintenance when pediatric rules do not apply.
Review the total deficit, remaining deficit, daily plan, and hourly rate.
Check the caution notes before using the estimate in any clinical workflow.

Frequently Asked Questions

1. What does this calculator estimate?

It estimates fluid deficit, remaining deficit after a bolus, maintenance needs, ongoing losses, and a simple hourly replacement rate for educational planning.

2. Which method should I choose?

Use clinical dehydration when you have an estimated percentage, weight loss when you know pre-illness and current weight, and free water deficit for hypernatremia.

3. Why does one percent dehydration equal 10 mL/kg?

A one percent acute body weight loss roughly equals ten milliliters per kilogram of fluid loss. This makes bedside dehydration estimates easier.

4. Does free water deficit equal total fluid deficit?

No. Free water deficit reflects water shortage relative to sodium. Isotonic deficit, ongoing losses, and resuscitation needs may differ.

5. Why include maintenance fluids?

Deficit replacement alone may miss baseline daily requirements. Maintenance adds expected routine needs so the total plan is more complete.

6. Can I use this for neonatal or critical care patients?

Use caution. Neonatal, renal, cardiac, shock, and intensive care cases often need individualized protocols, closer monitoring, and specialist oversight.

7. Why is the replacement period important?

The chosen time window changes the hourly rate. Faster correction can be unsafe in some electrolyte disorders, especially hypernatremia.

8. What should I verify before acting on the result?

Confirm weight accuracy, laboratory values, hemodynamics, urine output, comorbid disease, and whether losses are ongoing or already corrected.