Historical research profile. William E. Segar is not affiliated with or endorsed by MedMaths.
Pediatrics and fluid/electrolyte physiology
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William E. Segar, MD (1923–2021), was an American paediatrician, researcher and educator. His career included appointments at Indiana University and the University of Wisconsin–Madison, where he chaired the Department of Pediatrics from 1974 to 1985. With Malcolm A. Holliday, he co-authored the landmark 1957 paper on maintenance water needs in children.
Formula history
Formula originally described by William E. Segar.
Used for: Historical maintenance-water method; MedMaths UI is restricted to children aged 28 days to 18 years because neonatal and adult fluid therapy require age-appropriate guidance
Evidence trail
Holliday MA, Segar WE. Holliday MA, Segar WE — The maintenance need for water in parenteral fluid therapy. Pediatrics. 1957;19(5):823-832
The 1957 Pediatrics paper related maintenance water requirements to caloric expenditure and underlies the daily 100-50-20 bands. MedMaths does not use this paper to claim that Holliday and Segar published or invented the later rounded 4-2-1 hourly shorthand.
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Continue with the explanation
These guides explain the calculation, comparison or interpretation questions connected to this research history. This researcher profile provides background on the published work; it is not a calculator or clinical recommendation.
100-50-20 is the Holliday-Segar daily maintenance method; 4-2-1 is a rounded hourly shortcut based on the same weight bands. This guide explains the relationship, why the totals can differ, and the clinical limits of full maintenance.
Open guideUnderstand what the 100-50-20 rule estimates, why the first, second and later kilograms use different daily amounts, where the Holliday-Segar method came from, and what the result does not tell you by itself.
Open guideUnderstand why the 4-2-1 rule uses 4, 2 and 1 mL/kg/hr, how it relates to the daily Holliday-Segar method, how the stepped bands work, and why rounded hourly totals can differ from 100-50-20.
Open guideContinue exploring
Known for
Holliday-Segar daily maintenance-water method (100-50-20)
This source-based research reference profile draws on the original publications above and verified external sources. William E. Segar is not affiliated with or endorsed by MedMaths. Unconfirmed fields are left blank rather than estimated.
Reference data verified: 2026-08-11
See the methodology and editorial policy for the wider sourcing process.
