Maintenance Fluid Calculator (Pediatric & Adult)

Pediatric method and boundaries

Why 4-2-1 and 100/50/20 differ

Dividing the daily segment rates by 24 gives approximately 4.17, 2.08, and 0.83 mL/kg/hr. The 4-2-1 shortcut simplifies those segments to 4, 2, and 1, so its ×24 result does not always equal the daily formula. [1, 6]

NICE provides age-banded daily volumes for term neonates from birth through day 28; this page does not implement those formulas. The AAP composition guideline covers ages 28 days through 18 years and has defined exclusions, but those limits apply to its composition recommendation rather than every Holliday–Segar volume calculation. Pediatric and adult services can overlap at ages 16–18, so the local protocol determines which framework to use. [2, 3]

The Royal Children’s Hospital guideline, updated January 2026, treats IV fluid as a prescribed medication, prefers enteral hydration when possible, and uses full maintenance as a starting reference. Its local protocol notes that many unwell children need less than full maintenance, commonly about two-thirds, with serial weight and electrolyte monitoring. This calculator does not add an automatic two-thirds mode or decide whether restriction applies. [4]

NICE uses 100/50/20 for volume and separately addresses isotonic fluid composition. The 2018 AAP guideline addresses tonicity and composition for its covered population; it is not the source of the 4-2-1 or 100/50/20 rate formulas and does not establish an optimal maintenance rate. This page does not select a solution, electrolyte, or dextrose amount. [2, 3]

NICE notes that over 24 hours males rarely need more than 2500 mL and females rarely need more than 2000 mL. RCH uses a different local reference of 100 mL/hr or 2400 mL/day above 60 kg and advises considering ideal body weight. These are source-specific practice limits, not universal transformations of the Holliday–Segar formula. This page applies no automatic cap or weight substitution. [2, 4]

Adult NICE maintenance boundaries

The 25–30 mL/kg/day and lower 20–25 mL/kg/day references are displayed separately with their hourly equivalents. This page does not select a range. NICE advises considering ideal body weight and lower volumes in obesity and notes that adults rarely need more than 3 L/day; the calculator does not apply an automatic cap. [5]

NICE initial routine maintenance also considers approximately 1 mmol/kg/day each of sodium, potassium, and chloride, plus 50–100 g/day glucose. This page does not calculate or recommend those amounts, select fluid bags, or infer electrolyte additions from a water-volume result. An actual prescription requires monitoring and reassessment. [5]

What this calculator does not calculate

• Resuscitation, dehydration deficit, replacement of ongoing losses, or redistribution.
• Neonatal fluid calculations.
• Non-human maintenance-fluid calculations.
• Selecting fluid type, electrolytes, or glucose.
• Self-directed IV fluid use or generation of a final prescription.

All oral, enteral, medication, nutrition, blood-product, and other IV volumes must be considered in the actual plan.

Related calculators

• IV Drip Rate Calculator — need drops/min or tubing drop-factor calculations? That separate tool converts an already selected volume, time, and labeled tubing factor; it does not determine whether the volume is appropriate.
• Pediatric Dehydration Calculator addresses a dehydration deficit, which is separate from routine maintenance.
• Ideal Body Weight Calculator provides a separate reference when an applicable adult protocol explicitly requires ideal weight; this page cannot decide whether to use it.