Maintenance Fluid Rate Calculator

1. 1Enter weight (kg).
2. 2Enter temperature above 37.5°c (0 if afebrile) (°C over).
3. 3Read your hourly maintenance rate on the right — it updates as you type.
4. 4Hit Share to keep the scenario or send it to someone.

About this calculator

The Holliday-Segar method, commonly remembered as the "4-2-1 rule," estimates baseline maintenance fluid needs from body weight alone: 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 after that. It was originally derived from caloric expenditure in children but is used across pediatrics and adults as a simple starting point for patients who are NPO or otherwise not meeting fluid needs orally, absent other losses. It assumes normal renal function, no fever, no significant ongoing losses (vomiting, diarrhea, drains, burns), and euvolemia at baseline — none of which is guaranteed in a sick patient, so this number is a starting point that must be adjusted for fever (roughly +10-12% per degree C above 37.5), ongoing losses, or third-spacing. In adults, many clinicians simplify to roughly 25-30 mL/kg/day for maintenance rather than the full stepwise Holliday-Segar calculation, and this tool shows both. This tool is for education and workflow support only — not medical advice. Always verify results with a clinician and use clinical judgment alongside your institution's protocols.

What each field means

FAQ

Accuracy and limitations

• Population formulas describe averages; individual bodies vary, especially at the extremes of height, age, or muscle mass.
• Results do not account for medical conditions, medication, or pregnancy.
• Use this as a directional reference, not a diagnosis — talk to a clinician before acting on it.