Maintenance Fluid Calculator

This page works out maintenance fluid volume for an adult using the Holliday-Segar rule. You enter a body weight in kilograms or pounds, and it returns the hourly rate from the 4-2-1 form of the rule and the daily volume from the 100-50-20 form, with the band arithmetic and the gap between the two shown. The two forms disagree because 4-2-1 is the daily rule divided by 24 and rounded up, and that difference is printed rather than hidden. It is a starting estimate only: it takes no account of existing deficits, ongoing losses, fever, or cardiac and renal state, it names no fluid, and weights below 40 kg are refused because paediatric fluid is a prescribing decision.