Maintenance IV Fluid Calculator
The Holliday-Segar method, published in 1957, provides a widely used formula for estimating maintenance intravenous fluid requirements based on body weight. The 4-2-1 rule calculates an hourly rate: 4 mL/kg/hr for the first 10 kg, 2 mL/kg/hr for the next 10 kg, and 1 mL/kg/hr for each kilogram beyond 20 kg. This gives a practical bedside estimate applicable to pediatric and adult patients. The daily equivalent (100-50-20 rule) gives the same result over 24 hours. Actual fluid orders must account for clinical factors including temperature, ongoing losses, cardiac and renal function, and the specific type of fluid. This tool is for educational and reference purposes only.
4-2-1 rule formula
Rate (mL/hr) = 4 x first 10 kg + 2 x next 10 kg + 1 x remaining kg
Daily (mL/day) = Rate x 24
For a 70 kg patient: (4 x 10) + (2 x 10) + (1 x 50) = 40 + 20 + 50 = 110 mL/hr, giving 2,640 mL/day. The equivalent 100-50-20 daily rule gives: (100 x 10) + (50 x 10) + (20 x 50) = 1,000 + 500 + 1,000 = 2,500 mL/day (minor rounding difference at large weights due to hourly rounding).
Clinical considerations
- These rates are starting estimates; adjust for fever (+10-12% per degree Celsius above 38 C), humidity, burns, renal failure, and cardiac output.
- Neonates (less than 28 days) have different fluid requirements and are not well served by this rule.
- For pediatric patients, current guidelines favor isotonic maintenance fluids to reduce hyponatremia risk.
- Always verify fluid type, rate, and electrolyte composition with the treating clinical team.
Frequently asked questions
What is the 4-2-1 rule for maintenance fluids?
The Holliday-Segar 4-2-1 rule calculates hourly fluid requirements: 4 mL/kg/hr for the first 10 kg of body weight, plus 2 mL/kg/hr for the next 10 kg (11-20 kg), plus 1 mL/kg/hr for each kg above 20 kg. This rule was derived from caloric expenditure data in 1957 and is widely used in clinical practice.
How is daily maintenance fluid calculated?
The daily equivalent of the 4-2-1 rule is 100 mL/kg for the first 10 kg, plus 50 mL/kg for the next 10 kg, plus 20 mL/kg for each kg above 20 kg. This is sometimes called the 100-50-20 rule. Both methods give identical results.
Is the 4-2-1 rule appropriate for all patients?
The 4-2-1 rule provides a starting estimate. Fluid requirements are modified by clinical status, including fever, burns, renal function, cardiac function, and ongoing losses. Critically ill patients may need more or less than calculated maintenance rates. Electrolyte type and concentration must also be prescribed separately.
What IV fluid is typically used for maintenance?
For pediatric patients, balanced isotonic solutions (e.g., lactated Ringer's or 0.9% NaCl) are now preferred over hypotonic solutions due to the risk of hyponatremia. For adults, isotonic crystalloids are standard. The choice of fluid depends on the clinical scenario and electrolyte status.
Does the 4-2-1 rule apply to adults?
Yes, the formula applies across all ages. For a 70 kg adult: 4 x 10 + 2 x 10 + 1 x 50 = 40 + 20 + 50 = 110 mL/hr. However, adult maintenance fluid needs are often assessed differently in critical care, and clinical judgment is essential.
Official sources
- NIH National Library of Medicine: Holliday-Segar Method (original paper reference, PubMed).
- American Academy of Pediatrics: Fluid and Electrolytes in Pediatrics.
Reviewed by the CalculatorHub team, edited by James Graham, 15 June 2026. See our methodology.