What Is the Holliday-Segar Maintenance Fluid Rate Calculator?
The Holliday-Segar formula — widely known as the "4-2-1 rule" — is the standard bedside method for estimating maintenance intravenous fluid rates from body weight alone. Published in 1957, it remains a core part of pediatric and general clinical training because it closely tracks metabolic (caloric) demand, which fluid needs are based on.
This calculator applies the rule automatically: enter a weight, and it returns the maintenance rate in mL/hr along with the resulting 24-hour fluid volume.
How to Read Your Results
Maintenance Fluid Rate
The estimated hourly IV fluid rate in mL/hr, calculated from the weight-banded 4-2-1 rule.
Daily Fluid Volume
The hourly rate multiplied by 24, showing the total estimated maintenance fluid volume over a full day.
Weight Used
Your entered weight, converted to kilograms for the calculation, shown for confirmation.
Real-World Example
A patient weighs 24 kg.
| Weight Band | Rate | Subtotal |
|---|---|---|
| First 10 kg | 4 mL/kg/hr | 40 mL/hr |
| Next 10 kg (10–20 kg) | 2 mL/kg/hr | 20 mL/hr |
| Remaining 4 kg (20–24 kg) | 1 mL/kg/hr | 4 mL/hr |
| Total | 64 mL/hr |
A 64 mL/hr maintenance rate works out to 1,536 mL over 24 hours — the starting point a clinician would then adjust for the patient's actual fluid status, losses and comorbidities.
Tips for Using This Calculator
- This is a maintenance estimate only — it assumes euvolemia and does not account for dehydration, ongoing losses, fever, or third-spacing.
- Always apply clinical judgment and institutional protocols; the 4-2-1 rule is a starting point, not a prescription.
- The formula was derived largely from pediatric data and is most commonly applied in pediatric and neonatal settings, though the same weight-banded logic is sometimes extrapolated in adults.
- Renal, cardiac or hepatic impairment often requires downward adjustment regardless of the calculated rate.
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Last updated: August 2026 · Reviewed by: Simple Calculator Tools Editorial Team