The Holliday-Segar method
Malcolm Holliday and William Segar published this method in 1957. It calculates maintenance fluid requirements from metabolic expenditure rather than body weight alone. The underlying principle: for every 100 kcal a child burns, they need 100 mL of water.
The 4-2-1 rule is a bedside shortcut derived from it. Works well for most children between 3 and 50 kg. Outside that range, results are less reliable and clinical adjustment is needed.
The 4-2-1 rule
| Weight segment | Fluid per hour | Fluid per day |
|---|---|---|
| First 10 kg | 4 mL/kg/hr | 100 mL/kg/day |
| Next 10 kg (10-20 kg) | 2 mL/kg/hr | 50 mL/kg/day |
| Each kg above 20 kg | 1 mL/kg/hr | 20 mL/kg/day |
When to adjust
These are maintenance estimates for a well child. Fever adds roughly 12% per degree above 38°C. Significant insensible losses from burns, open wounds, or high ambient temperature push requirements up. SIADH, renal failure, or heart failure often require restriction to 60-75% of maintenance. Always reassess based on urine output, weight, and clinical response.
Dehydration replacement
The deficit volume is weight loss in kg, multiplied by 1,000 mL. A 15 kg child with 10% dehydration has lost approximately 1.5 kg of fluid, so 1,500 mL deficit. Half is typically replaced in the first 8 hours, the remainder over the next 16. This runs alongside maintenance fluids, not instead of them.
Severe dehydration (15%) with haemodynamic compromise needs an immediate 20 mL/kg bolus of isotonic saline before starting structured replacement. That comes before any calculation from this tool.
Related tools on MediCalc Pro
For weight-based drug dosing, see Pediatric Dose Calculator. For IV infusion rate calculation, see IV Drip Rate Calculator. For volume unit conversions (mL to fl oz), see Volume Converter. For growth monitoring, see Growth Chart Percentile. For adult daily water intake, see Daily Water Intake Calculator.
References
- Holliday MA, Segar WE. "The maintenance need for water in parenteral fluid therapy." Pediatrics. 1957;19(5):823-832.
- National Institute for Health and Care Excellence. IV fluids in children: intravenous fluid therapy in children and young people in hospital. NICE guideline NG29, 2020.
- Roberts KB. "Fluid and electrolytes: parenteral fluid therapy." Pediatr Rev. 2001;22(11):380-386.