Holliday-Segar Maintenance Fluids Calculator (Paediatric 4-2-1 Rule)

How it works

Per day: 100 mL/kg for the first 10 kg + 50 mL/kg for the next 10 kg + 20 mL/kg above 20 kg. Per hour (4-2-1): 4 mL/kg + 2 mL/kg + 1 mL/kg. Usual cap ≈ 2,400 mL/day (100 mL/h). Deficit (mL) = weight × % dehydration × 10. GIR (mg/kg/min) = glucose % × 10 × mL/h ÷ 60 ÷ kg. Drops/min = mL/h × drops per mL ÷ 60

Holliday and Segar linked water needs to calorie expenditure in 1957 and produced the tiered per-kilogram rule that paediatricians still use: 100 mL/kg/day for the first 10 kg, 50 for the next 10, 20 thereafter — or, hour by hour, 4-2-1. The hourly version is a rounding of the daily one, so the two can differ by a few mL/h. Because the rule keeps climbing with weight, maintenance is usually capped at about 2–2.5 L a day (around 100 mL/h) for adolescents and adults; the cap is adjustable here. It estimates the water lost through breathing, skin and urine in a resting child; fever, tachypnoea, burns and diarrhoea raise it, while ventilation, humidified air, renal failure and high ADH states lower it, which is why restricted (often 2/3) maintenance is common. The bigger modern change is what fluid to use: hypotonic solutions, once standard, caused hospital-acquired hyponatraemia, so isotonic fluids with glucose are now recommended. Any dehydration deficit (weight × % × 10 mL) is added on top — minus boluses already given — and replaced over 24 hours, half in the first 8 hours, or over 48 hours in hypernatraemic dehydration, plus measured ongoing losses. The calculator also shows the drip rate, glucose infusion rate, sodium delivered by the chosen fluid and the daily sodium and potassium requirement.

Worked example

An 18 kg child: 10 × 4 + 8 × 2 = 56 mL/h (10 × 100 + 8 × 50 = 1,400 mL/day; 1,400 ÷ 24 = 58.3 mL/h). With 5% dehydration the 900 mL deficit brings the 24-hour total to 2,300 mL, about 96 mL/h. Replacing half the deficit in 8 hours gives 56 + 450 ÷ 8 ≈ 112 mL/h for 8 hours, then 56 + 450 ÷ 16 ≈ 84 mL/h for 16 hours. A 70 kg adolescent would get 110 mL/h by 4-2-1, capped at 100 mL/h (2,400 mL/day).

Sources: Holliday MA, Segar WE (1957) — The maintenance need for water in parenteral fluid therapy (Pediatrics) · NICE NG29 — Intravenous fluid therapy in children and young people in hospital · Feld LG et al. (2018) — AAP clinical practice guideline: maintenance intravenous fluids in children

Frequently asked questions