Understanding What is the 100 50 20 Rule in Medications and Fluid Management

October 12, 2025 •

2 min read

The Holliday-Segar formula, more commonly known as the 100 50 20 rule, was developed over half a century ago and remains a fundamental method in pharmacology and pediatric medicine for calculating a child's daily intravenous fluid needs based on their weight. This guideline helps healthcare professionals ensure appropriate hydration and electrolyte balance for young patients who cannot consume fluids orally.

Quick Summary

The 100-50-20 rule provides a structured method for estimating the daily maintenance fluid needs of a pediatric patient based on their weight in kilograms, a core principle in medical and pharmacological practice.

Key Points

Foundation of Pediatric Fluid Management: The 100 50 20 rule, also known as the Holliday-Segar formula, is a standard method for estimating daily maintenance fluid needs for infants and children.
Weight-Based Tiers: The rule assigns estimated fluid volumes per kilogram of body weight, depending on the patient's weight bracket (0-10 kg, 11-20 kg, >20 kg).
Hourly Conversion: The rule has a related hourly estimation, sometimes referred to as the 4-2-1 rule, which is used for estimating IV infusion rates in clinical practice.
Approximation, Not Absolute: The formula provides a baseline estimate based on metabolic rate and should be adjusted by clinicians for various factors like fever, burns, or renal function.
Electrolyte and Fluid Type: Beyond volume, the specific type of intravenous fluid and electrolyte content must be carefully considered, especially in light of risks like hyponatremia.
Obesity Consideration: For obese patients, healthcare providers may need to use ideal body weight rather than actual body weight to help prevent fluid overload.

Origins and Purpose of the 100 50 20 Rule

First described by pediatricians Malcolm Holliday and William Segar in 1957, the 100 50 20 rule is used to estimate a child's daily water and electrolyte needs based on their metabolic rate and weight. This formula simplifies the non-linear relationship between weight and fluid requirements into three weight-based tiers. It's particularly useful when children cannot take fluids orally, such as during illness or surgery.

How to Apply the Holliday-Segar Formula

The 100 50 20 rule estimates the total daily fluid volume needed over 24 hours based on the child's weight in kilograms. The estimation involves different rates for different weight ranges:

For the first 10 kg of body weight, an estimated volume is used.
For the next 10 kg (for weights between 11 and 20 kg), a different estimated volume is applied per kilogram.
For the remaining weight (for every kg over 20 kg), a further estimated volume is used per kilogram.

The Relationship to the 4-2-1 Rule

The 100-50-20 rule can be related to an hourly rate estimation, sometimes referred to as the 4-2-1 rule, which is often used in anesthesia and intensive care settings for continuous fluid infusions. This related rule is:

An estimated rate per kilogram per hour for the first 10 kg.
A different estimated rate per kilogram per hour for the next 10 kg.
A further estimated rate per kilogram per hour for each kg over 20 kg.

Clinical Considerations and Modern Application

While the 100 50 20 rule provides a baseline estimation, modern clinical practice emphasizes tailoring fluid therapy to the individual patient. This includes selecting the appropriate type and composition of intravenous fluid to avoid complications like hyponatremia. Adjustments to the standard estimation may be needed for various factors:

Conditions increasing fluid loss, such as fever or burns.
Conditions decreasing fluid needs, like high humidity or renal impairment.
For obese patients, ideal body weight may be used to prevent over-hydration.

Comparison of the 100 50 20 and 4 2 1 Rules

This table summarizes the key differences between the daily and hourly applications of the fluid calculation principle.


Feature	100 50 20 Rule (Holliday-Segar)	4 2 1 Rule
Timeframe	24-hour total fluid volume estimation	Hourly infusion rate estimation
Calculation Method	Sum of daily fluid volume estimations per weight tier	Sum of hourly fluid rate estimations per weight tier
Primary Use	Standard estimation for total daily maintenance fluid	Related hourly estimation for IV infusion rate
Fluid Units	Milliliters per day (mL/day) estimation	Milliliters per hour (mL/hr) estimation
Relationship	The basis for the related hourly rule	A direct, convenient relationship to the daily rule

Conclusion

The 100 50 20 rule is a vital tool in pediatric fluid management, offering a standardized approach to estimating baseline maintenance fluid needs. While its core principles remain relevant, clinical judgment is crucial for adjusting estimations and selecting appropriate fluid types based on individual patient circumstances. The related 4-2-1 rule further enhances the practical application of this foundational pharmacological concept in acute care settings. More details on this method can be found in authoritative medical sources.

Frequently Asked Questions

The rule was developed by pediatricians Malcolm Holliday and William Segar, and their work was published in 1957. It is often referred to as the Holliday-Segar formula.

Yes, it is still a widely used and accepted method in pediatric medicine for estimating baseline maintenance fluid requirements, though clinicians always consider individual patient factors for modifications.

The tiered structure accounts for the non-linear relationship between weight and metabolic rate. Smaller infants have a higher metabolic rate per kilogram, potentially requiring a relatively larger fluid estimation per kilogram, while larger children's metabolic rate per kilogram decreases.

The 4-2-1 rule is related to the hourly equivalent of the 100-50-20 rule. It provides an easier bedside estimation for setting IV fluid infusion rates. It involves different estimated rates per kilogram per hour based on weight tiers.

Adjustments may be necessary for patients with increased fluid needs (e.g., fever, burns) or decreased needs (e.g., renal impairment, humidified ventilation). For obese patients, ideal body weight may be used instead of actual weight.

No, the rule is specifically for infants and children. Maintenance fluid requirements for adults are typically estimated differently, sometimes using formulas like 25-30 mL/kg/day.

The rule only estimates baseline maintenance fluid needs. It does not account for additional fluids that may be required for special circumstances, such as replacing fluid lost due to vomiting, diarrhea, or blood loss.