Holliday-Segar Maintenance Fluids Calculator (4-2-1 Rule)
The Holliday-Segar method estimates daily maintenance fluid requirements by weight — 100 mL/kg for the first 10 kg, 50 mL/kg for the next 10 kg, and 20 mL/kg for each kilogram over 20 kg — equivalent to the hourly "4-2-1" rule (4, then 2, then 1 mL/kg/hr).
Quick answer
The Holliday-Segar method estimates daily maintenance fluids by weight: 100 mL/kg for the first 10 kg, 50 mL/kg for the next 10 kg (11–20 kg), and 20 mL/kg for each kilogram over 20 kg. The equivalent hourly "4-2-1" rule gives 4, then 2, then 1 mL/kg/hr across the same weight bands.
Maintenance fluid input
Daily method: 100 mL/kg for the first 10 kg, 50 mL/kg for 11–20 kg, 20 mL/kg for each kg over 20 (the hourly "4-2-1" rule).
How to use the Holliday-Segar calculator
- 1Enter the body weight. Enter the patient’s weight in kilograms.
- 2Read the daily and hourly volumes. The tool applies the 100/50/20 mL/kg/day method and shows the maintenance fluid in mL/day and the equivalent mL/hr (the "4-2-1" rate).
- 3Use it as a starting estimate. Maintenance fluids are a baseline; deficits, ongoing losses and the patient’s clinical state are added or adjusted by a clinician.
Medical disclaimer: This is general health information, not medical advice. It does not diagnose or treat any condition, and the results are estimates based on public reference formulas. Always consult a qualified doctor about your individual health. If you think you may have a medical emergency, contact your local emergency services immediately.
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Book a consultationFrequently asked questions
What is the 4-2-1 rule for fluids?⌄
The 4-2-1 rule is the hourly version of the Holliday-Segar method: 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 kilogram over 20 kg. It gives the same total as the 100/50/20 mL/kg/day method.
Does Holliday-Segar work for adults?⌄
The method was derived in children but the weight-based formula is sometimes applied to estimate baseline maintenance in adults too. In practice adult maintenance is often capped and adjusted for comorbidity, so a clinician interprets it in context.
Does this account for dehydration?⌄
No. Holliday-Segar estimates ongoing maintenance needs only. Any existing fluid deficit and continuing abnormal losses (for example from vomiting, diarrhoea or fever) must be calculated and replaced separately.
Is my data stored?⌄
No. The calculator runs entirely in your browser; nothing you enter is sent to a server.
Sources & validation
This calculator reproduces the published Holliday-Segar score, validated for estimated daily/hourly maintenance fluid requirement by body weight.
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