Dosing
Maintenance fluids calculator
One weight in, two numbers out: the hourly rate for the pump and the 24-hour volume for the chart — by the rule every ward already speaks.
A 25 kg child needing intravenous maintenance while nil by mouth.
65 mL/h — 1,600 mL over 24 hours
The pump rate and the daily volume from one entry: 40 + 20 + 5 mL/h across the three weight tiers, maintenance only, before any deficit or ongoing losses.
Who this is for
For paediatric, emergency, and ward clinicians writing maintenance fluid prescriptions. The Holliday-Segar tiers — 4 mL/kg/h for the first 10 kg, 2 for the next 10, 1 thereafter — are easy to misadd at 3 am; the tool computes the hourly rate and the matching 100-50-20 daily volume from a single weight, for infants through adults.
How it works
What it calculates
Maintenance fluid requirements by the Holliday-Segar rules: 4-2-1 mL/kg/h by weight tier for the hourly rate, and 100-50-20 mL/kg for the 24-hour volume.
What it does not cover
Maintenance only — resuscitation boluses, deficit replacement, and ongoing losses are calculated and added separately. Neonates follow day-of-life regimens, and adults are commonly capped around 100 mL/h.
Worth remembering
Maintenance fluid is a prescription like any drug: review daily, watch the electrolytes, and stop when the patient drinks. Reference: Holliday & Segar, Pediatrics 1957.
Built on published evidence
- Holliday & Segar, Pediatrics 1957
Codification last reviewed 2026-08-28, and checked against published reference values in automated tests on every release — see the full evidence ledger.
Questions clinicians ask
How does the 4-2-1 rule work?
4 mL/kg/h for the first 10 kg, plus 2 mL/kg/h for the next 10 kg, plus 1 mL/kg/h for every kilogram above 20 — the hourly form of Holliday and Segar's 100-50-20 daily rule (Pediatrics, 1957).
Does this cover resuscitation or deficit replacement?
No — it is maintenance only. Resuscitation boluses, deficit correction, and ongoing losses are calculated and added separately, and neonates follow day-of-life regimens rather than 4-2-1.
Should adults really get the full 4-2-1 rate?
Often not — the formula gives 110 mL/h at 70 kg, and adults are commonly capped around 100 mL/h. The calculator notes the cap rather than silently applying it, so the prescription stays a clinical decision.
How often should a maintenance prescription be reviewed?
Daily, like any drug: check the electrolytes, reassess the indication, and stop the fluids as soon as the patient is drinking adequately. Maintenance fluid is a prescription, not a default.
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