Maintenance Fluids Calculator (Holliday-Segar / 4-2-1 Rule)
Enter the patient weight to calculate the recommended daily maintenance fluid volume and hourly infusion rate using the Holliday-Segar nomogram and the 4-2-1 rule. A standard bolus volume for fluid resuscitation is also provided. Switch between metric (kg) and imperial (lb) units, choose your preferred method, and see the full weight-segment breakdown in the "Show your work" panel. Suitable for pediatric and adult patients from 3.5 kg to 100 kg. Not validated for neonates under 28 days or patients below 3.5 kg.
What are maintenance fluids?
Maintenance fluids replace the body's baseline daily losses from urine output, insensible evaporation through the skin and lungs, and stool. These losses occur continuously and must be replenished to keep the patient in fluid balance. In clinical practice, maintenance fluids are given intravenously when a patient cannot drink adequately, for example during surgery, after anesthesia, or during acute illness. The standard composition is typically a hypotonic or isotonic crystalloid (such as 0.9% normal saline, lactated Ringer's, or a dextrose-saline mixture) chosen based on the patient's electrolyte status and clinical context.
The Holliday-Segar method and the 4-2-1 rule
Malcolm Holliday and William Segar published their landmark 1957 paper establishing that a child's fluid needs at rest closely track their caloric expenditure, roughly 100 mL of water per 100 kcal metabolized. This produced the now-standard three-tier nomogram: 100 mL/kg/day for the first 10 kg, 50 mL/kg/day for the next 10 kg, and 20 mL/kg/day for each kilogram above 20 kg. The 4-2-1 rule is a convenient bedside shorthand: 4 mL/kg/h for the first 10 kg, 2 mL/kg/h for the second 10 kg, and 1 mL/kg/h for each kilogram above 20 kg. The 4-2-1 tiers are the daily tiers divided by 24 and rounded to whole numbers, so the two rules agree closely but not exactly (the 4-2-1 rate runs a few mL/h above the Holliday-Segar daily volume divided by 24 once weight exceeds 20 kg). Clinicians use whichever is more convenient for the order being written.
Fluid bolus for resuscitation
A fluid bolus is not the same as maintenance fluids. Boluses are given rapidly (over 15-30 minutes) to correct acute hypovolemia, sepsis, or dehydration, while maintenance fluids run slowly over 24 hours to replace ongoing baseline losses. The standard bolus dose is 20 mL/kg of an isotonic crystalloid, capped at 1000 mL in practice. After each bolus the patient should be reassessed for response (improvement in heart rate, blood pressure, capillary refill, urine output) before repeating. Overaggressive bolus therapy has been associated with fluid overload, dilutional coagulopathy, and abdominal compartment syndrome in critically ill patients.
Clinical adjustments and limitations
The Holliday-Segar formula was derived from healthy resting children. Several patient populations require significant modifications. Febrile patients lose additional insensible fluid (roughly 10% extra per 1 degree Celsius above normal). Patients with burns have dramatically higher insensible losses. Patients with renal failure, heart failure, or liver cirrhosis may need restriction to 50-75% of calculated maintenance. Post-operative patients are at risk for hyponatremia from non-osmotic antidiuretic hormone (ADH) release, which concentrates urine and can cause dangerous water retention, so many guidelines now favor isotonic (not hypotonic) maintenance fluids in this setting. Finally, the formula should not be used in neonates under 28 days of age or in patients weighing less than 3.5 kg, who require specialized neonatal fluid protocols.
Holliday-Segar maintenance fluid tiers
| Weight range | Daily rate | Hourly rate (4-2-1) | Example (15 kg) |
|---|---|---|---|
| 0-10 kg | 100 mL/kg/day | 4 mL/kg/h | 1000 mL/day, 40 mL/h |
| 10-20 kg | 1000 + 50 mL/kg over 10 kg | 40 + 2 mL/kg/h over 10 kg | 1250 mL/day, 50 mL/h |
| 20-65 kg | 1500 + 20 mL/kg over 20 kg | 60 + 1 mL/kg/h over 20 kg | -- |
| >65 kg | Held at 2400 mL/day | Held at 105 mL/h | -- |
Standard Holliday-Segar rates for daily maintenance volume and hourly infusion rate by weight tier. The 4-2-1 hourly figures are rounded, so they run slightly above the daily volume divided by 24 (for example 50 mL/h versus 52.1 mL/h at 15 kg). The ceiling above 65 kg is a common clinical convention, not part of the 1957 nomogram.
Frequently asked questions
What is the 4-2-1 rule for maintenance fluids?
The 4-2-1 rule is a simple bedside formula for calculating the hourly intravenous fluid rate: 4 mL/kg/h for the first 10 kg of body weight, 2 mL/kg/h for the next 10 kg (10-20 kg), and 1 mL/kg/h for each kilogram above 20 kg. For example, a 25 kg child needs (10 x 4) + (10 x 2) + (5 x 1) = 65 mL/h. It is a rounded version of the Holliday-Segar daily volume divided by 24 (1600 mL/day / 24 = 66.7 mL/h), close enough for bedside pump orders.
How is the Holliday-Segar method different from the 4-2-1 rule?
They calculate the same thing in different units. Holliday-Segar gives the total daily volume in mL/day using the 100/50/20 tiers (100 mL/kg for the first 10 kg, 50 mL/kg for the next 10 kg, 20 mL/kg above 20 kg). The 4-2-1 rule gives the hourly infusion rate using 4/2/1 tiers, which are the daily tiers divided by 24 and then rounded (100/24 = 4.17, 50/24 = 2.08, 20/24 = 0.83). Because of that rounding the two methods agree closely but not exactly: a 15 kg child works out to 1250 mL/day (52.1 mL/h) by Holliday-Segar and 50 mL/h by the 4-2-1 rule. Clinicians often prefer the 4-2-1 rule when writing infusion pump orders.
Should I use actual or ideal body weight for obese patients?
Use ideal body weight for obese patients. Adipose tissue is metabolically much less active than lean tissue and does not generate proportionally higher fluid losses. Dosing maintenance fluids on actual weight in an obese patient risks fluid overload. Ideal body weight can be estimated using height-based formulas (for adults: approximately 50 kg + 2.3 kg per inch over 5 feet for males, 45.5 kg + 2.3 kg per inch for females).
Can this calculator be used for neonates?
No. The Holliday-Segar formula does not apply to neonates (infants under 28 days of age) or patients weighing less than 3.5 kg. Neonatal fluid requirements are much more complex, varying substantially by gestational age, postnatal day, environmental humidity (incubator use), and specific clinical conditions like transient tachypnea of the newborn or necrotizing enterocolitis. Neonatal fluid orders should always be developed using specialized neonatal protocols and reviewed by a neonatologist.
What type of fluid should be used for maintenance?
Current guidelines (including the 2015 NICE guidance and AAP recommendations) favor isotonic crystalloids such as 0.9% normal saline or lactated Ringer's for most pediatric and adult maintenance therapy, because hypotonic solutions (e.g., 0.45% saline) can cause hospital-acquired hyponatremia in patients with elevated ADH. Dextrose is often added (e.g., D5 0.9% NS) for patients who are fasting and need a carbohydrate substrate. The specific fluid type is a clinical decision based on serum electrolytes, clinical context, and physician judgment.
How often should maintenance fluid orders be reassessed?
At minimum every 24 hours, and more frequently in critically ill, post-operative, or hemodynamically unstable patients. Every reassessment should consider urine output (target 0.5-1.0 mL/kg/h in children, 0.5 mL/kg/h in adults), serum electrolytes, daily weight, and the patient's overall fluid balance. Maintenance fluids are not a "set and forget" order; many patients require dose adjustments as their clinical status evolves.