Maintenance Fluid Calculator
4-2-1 rule (Holliday-Segar method) for calculating maintenance IV fluid requirements in adults and pediatrics. Shows hourly rate, daily volume, and weight-bracket breakdown.
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Disclaimer: For educational purposes only. Adjust for clinical context (fever, burns, renal/cardiac disease). Not for resuscitation. Not a substitute for clinical judgment.
About This Tool
What Is the 4-2-1 Rule?
The 4-2-1 rule, also known as the Holliday-Segar method, is the most widely used formula for calculating maintenance intravenous fluid requirements. Published by Malcolm Holliday and William Segar in 1957 in Pediatrics, the method estimates insensible fluid losses based on metabolic rate, which correlates with body weight. The rule allocates 4 mL/kg/hr for the first 10 kg of body weight, 2 mL/kg/hr for the next 10 kg (11–20 kg), and 1 mL/kg/hr for each kilogram above 20 kg. The daily equivalent is 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 additional kg.
Practical Application
For a 70 kg adult, the 4-2-1 rule yields: (4 × 10) + (2 × 10) + (1 × 50) = 110 mL/hr or 2,640 mL/day. This is consistent with the commonly cited adult maintenance rate of approximately 2,000–2,500 mL/day. In pediatrics, the formula is essential because children have higher metabolic rates per kilogram and are more vulnerable to fluid imbalances. The calculated rate provides a starting point that should be adjusted for clinical conditions including fever, tachypnea, diarrhea, vomiting, and ongoing surgical or burn losses.
Fluid Composition
The choice of maintenance fluid varies by patient population and clinical context. Traditional adult maintenance consists of D5-0.45% NaCl with 20 mEq/L KCl. However, there has been a significant shift in pediatric practice toward isotonic maintenance fluids (0.9% NaCl or Ringer's lactate) following evidence that hypotonic fluids increase the risk of hospital-acquired hyponatremia, which can cause serious neurological complications. The NICE guidelines for adults recommend 25–30 mL/kg/day of fluid with 1 mmol/kg/day each of sodium, potassium, and chloride.
🔑 Clinical Pearls
- In pediatrics, use isotonic fluids (NS or LR) for maintenance to reduce hyponatremia risk — this is now standard of care.
- The 4-2-1 rule overestimates fluid needs in obese patients — consider using ideal body weight.
- Adjust for fever: increase by approximately 10% for each degree Celsius above 37°C.
- This formula estimates maintenance needs only. It does not replace resuscitation protocols for sepsis, hemorrhage, or burns.
- For perioperative maintenance, anesthesiologists commonly use the 4-2-1 rule as a baseline plus replacement of surgical losses.
- Reassess maintenance fluid orders daily — the most common IV fluid error is continuing maintenance fluids longer than necessary.
Key References
- Holliday MA, Segar WE. The maintenance need for water in parenteral fluid therapy. Pediatrics. 1957;19(5):823-832.
- McNab S, et al. 140 mmol/L of sodium versus 77 mmol/L of sodium in maintenance IV fluid therapy for children. Lancet. 2015;385(9974):1190-1197.
- NICE Guideline CG174: Intravenous fluid therapy in adults in hospital. 2013 (updated 2017).
Formula last verified: February 2026