What Is a Maintenance Fluid Calculator?
A maintenance fluid calculator estimates the intravenous (IV) fluid a patient needs to replace normal ongoing losses, based on body weight. It uses the widely taught 4-2-1 rule for hourly rates and the Holliday-Segar method for daily volumes. These tools are a staple of pediatric and general clinical care. Enter the patient's weight and the calculator returns the maintenance fluid rate per hour and per day.
How to Use the Calculator
- Enter the patient's weight in kilograms.
- Calculate — see the hourly maintenance rate (mL/hr) and the daily volume (mL/day).
The 4-2-1 Rule (Hourly Rate)
| Body Weight | Hourly Fluid |
|---|---|
| First 10 kg | 4 mL/kg/hr |
| Next 10 kg (11–20 kg) | 2 mL/kg/hr |
| Each kg above 20 kg | 1 mL/kg/hr |
For example, a 25 kg patient: (10 × 4) + (10 × 2) + (5 × 1) = 40 + 20 + 5 = 65 mL/hr.
The Holliday-Segar Method (Daily Volume)
The daily equivalent uses 100-50-20: 100 mL/kg/day for the first 10 kg, 50 mL/kg/day for the next 10 kg, and 20 mL/kg/day for each kilogram beyond 20 kg. A 25 kg patient needs (10 × 100) + (10 × 50) + (5 × 20) = 1,000 + 500 + 100 = 1,600 mL/day.
Important Considerations
- Maintenance fluids cover normal losses, not existing deficits or ongoing abnormal losses, which require additional replacement.
- Fluid choice, electrolytes, and rate must be individualized to the clinical situation.
- Reassess frequently — fever, vomiting, and other factors change needs.
Note: This calculator is an educational tool and does not replace clinical judgment, local protocols, or current guidelines.
Frequently Asked Questions
What is the 4-2-1 rule?
It estimates hourly maintenance fluid: 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 kg.
What is the Holliday-Segar method?
It estimates daily maintenance fluid using 100 mL/kg for the first 10 kg, 50 mL/kg for the next 10 kg, and 20 mL/kg for each kilogram beyond 20 kg.
Do maintenance fluids include deficits?
No — maintenance fluids replace normal ongoing losses only. Dehydration deficits and abnormal losses require additional replacement on top of maintenance.
Is the 4-2-1 rule only for children?
It is most commonly taught in pediatrics but the weight-based approach can apply broadly, with clinical adjustment for adults and specific conditions.
Is this maintenance fluid calculator free?
Yes — it is completely free, requires no signup, and gives hourly and daily estimates.