Maintenance Fluid Calculator
Work out a maintenance IV fluid rate from body weight with the Holliday-Segar method. Enter a weight to see the daily requirement by the 100-50-20 rule and the hourly rate by the 4-2-1 rule. These give normal maintenance water for a well child or adult — not fluid resuscitation and not replacement of an existing deficit or ongoing losses.
About maintenance fluids
The Holliday-Segar method ties maintenance water to metabolic rate, giving the familiar 100-50-20 daily rule and 4-2-1 hourly rate. It estimates normal ongoing needs and is a starting point that is reassessed against weight, urine output, electrolytes and clinical state. Source: Holliday MA, Segar WE, “The maintenance need for water in parenteral fluid therapy,” Pediatrics 1957;19(5):823–832.
Frequently asked questions
What is the Holliday-Segar formula?
The Holliday-Segar method estimates daily maintenance water from weight: 100 mL/kg for the first 10 kg, 50 mL/kg for the next 10 kg (10–20 kg), and 20 mL/kg for every kilogram above 20 kg. Add the bands for the total mL per day — this is the “100-50-20 rule”. It was published by Holliday and Segar in 1957 from the relationship between body weight and metabolic rate.
What is the 4-2-1 rule?
The 4-2-1 rule is the hourly version of Holliday-Segar: 4 mL/kg/hr for the first 10 kg, 2 mL/kg/hr for the next 10 kg, and 1 mL/kg/hr for each kg above 20 kg. For a 22 kg child that is (4×10) + (2×10) + (1×2) = 62 mL/hr. The daily and hourly rules do not divide exactly — 100 mL/kg/day is 4.17 mL/kg/hr, not 4 — so the mL/day figure is a few percent higher than the 4-2-1 rate × 24.
Does this apply to adults?
The formula can be applied at any weight, but it was derived in children and tends to over-estimate needs in larger adults, where maintenance is usually individualised and often capped (many services cap around 2,000–2,500 mL/day for an average adult, or prescribe roughly 25–30 mL/kg/day). Use local guidance for adult maintenance. This calculator shows the raw Holliday-Segar figures so you can see the underlying numbers.
What is this NOT for?
Maintenance fluids replace normal ongoing water and electrolyte losses in someone who is not volume-depleted. They are not resuscitation fluids for shock or severe dehydration, and they do not include replacement of an existing fluid deficit or of continuing losses such as vomiting, diarrhoea, drains or fever. Those are calculated and added separately, and the plan is reassessed as the clinical picture changes.
What fluid and how is it monitored?
Maintenance is a rate, not a prescription on its own — the choice of fluid (for example an isotonic solution with dextrose, and added potassium once urine output is confirmed) and the monitoring of weight, electrolytes and fluid balance follow local protocol. Hypotonic maintenance fluids in children have been linked to hyponatraemia, which is why isotonic fluids are now generally preferred. This calculator is an educational reference, not medical advice.
This is a reference tool, not a diagnosis or medical advice. Results depend on the laboratory, assay and clinical context, and reference intervals vary between labs and by age and sex — always read your result against the range printed on your own report and discuss it with a qualified healthcare professional.
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