Maintenance Fluid Calculator (Holliday-Segar)
Enter body weight to get the hourly and daily maintenance fluid rate by the Holliday-Segar method.
Educational use only — not medical advice. This tool is for education only and uses the standard Holliday-Segar method. It is not medical advice and does not replace clinical judgment, which must account for the patient's condition, losses and electrolytes. Always confirm fluid orders with a qualified clinician.
The Holliday-Segar method estimates maintenance fluids from body weight. The hourly '4-2-1' rule gives 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 above 20. The daily version uses 100, 50 and 20 mL/kg for the same weight bands.
⚠️ Double-check important results. This is an educational estimate, not professional advice — and where it uses a rate, bracket or fee, those change over time. Verify anything you'll rely on, especially in legal, financial, tax or medical matters, and read our full disclaimer. Think a result is wrong? Tell us so we can fix it.
How to Use This Calculator
Enter the patient's weight in kilograms. The calculator applies the Holliday-Segar method and returns both the hourly maintenance rate (the 4-2-1 rule, used to set an infusion) and the total daily maintenance volume.
Maintenance fluids replace the water a patient normally loses through urine, breathing and the skin. The method is a starting estimate for an otherwise stable patient and does not include replacement of abnormal losses.
How the Calculation Works
The body needs proportionally less fluid per kilogram as it gets larger, so the method uses three weight bands. For the hourly rate, the first 10 kg get 4 mL/kg/hr, the next 10 kg get 2 mL/kg/hr, and every kilogram above 20 gets 1 mL/kg/hr.
The daily rate follows the same idea with 100, 50 and 20 mL/kg per day for the three bands. Both come from the original Holliday-Segar work and give consistent results.
hourly = 4·(≤10kg) + 2·(10–20kg) + 1·(>20kg)
Worked Example
For a 25 kg child: the first 10 kg give 4 × 10 = 40 mL/hr, the next 10 kg give 2 × 10 = 20 mL/hr, and the remaining 5 kg give 1 × 5 = 5 mL/hr. The total hourly rate is 40 + 20 + 5 = 65 mL/hr.
The daily total is 100 × 10 + 50 × 10 + 20 × 5 = 1,000 + 500 + 100 = 1,600 mL per day.
Assumptions and Limitations
- Uses the Holliday-Segar method for maintenance needs only
- Does not replace ongoing abnormal losses (fever, vomiting, drains)
- Assumes a stable patient with normal kidney function
- Clinical judgment and electrolytes must guide any real order
Who Uses a Maintenance Fluid Calculator
Nursing and medical students use this to estimate daily and hourly maintenance IV fluids with the 4-2-1 rule, especially for pediatric cases. It supports coursework, rounds preparation, and quick reference. Treat it as an educational estimate to understand the method, always confirmed against clinical guidelines and a supervising clinician.
Related Calculators
mg to mL Calculator
Convert a drug dose in milligrams to a volume in millilitres using its concentration.
Open calculator →IV Drip Rate Calculator
Find IV drip rate in drops per minute and mL per hour.
Open calculator →Tidal Volume Calculator
Lung-protective tidal volume from ideal body weight.
Open calculator →Steps to Miles Calculator
Convert step count to miles using your height-based stride.
Open calculator →Frequently Asked Questions
What is the Holliday-Segar method?
It is a standard way to estimate a patient's maintenance fluid needs from body weight, using the 4-2-1 rule per hour or the 100-50-20 rule per day across three weight bands.
What is the 4-2-1 rule?
It gives the hourly maintenance rate: 4 mL/kg/hr for the first 10 kg, 2 mL/kg/hr for the next 10 kg, and 1 mL/kg/hr for every kilogram above 20.
How much maintenance fluid does a 25 kg child need?
By the 4-2-1 rule, 40 + 20 + 5 = 65 mL/hr, or about 1,600 mL over 24 hours by the 100-50-20 daily rule.
Does this include fluid for dehydration?
No. It calculates maintenance only. Deficits from dehydration and ongoing losses from fever, vomiting or drains must be added separately by a clinician.
Is Holliday-Segar used for adults?
It is most commonly taught for pediatric fluids, but the same weight-band logic can estimate maintenance in adults. Real adult fluid management relies heavily on clinical assessment.
Looking for a different calculator?
CalculatorPlus has free tools across finance, construction, math, health and more — each one showing the formula and a worked example.