Maintenance IV Fluid (4-2-1) Calculator

About this calculator

The Holliday-Segar 4-2-1 rule, published by Malcolm Holliday and William Segar in 1957, estimates the hourly maintenance intravenous fluid rate a patient needs based purely on body weight: 4 mL/kg/hr for the first 10 kg of weight, 2 mL/kg/hr for the next 10 kg, and 1 mL/kg/hr for every kilogram above 20. It was derived from the observation that metabolic rate, and therefore fluid and calorie turnover, scales with body weight in a predictable, tiered way rather than linearly across the whole weight range.

Pediatricians, nurses, and anesthesiologists use the 4-2-1 rule constantly to set IV drip rates for patients who aren’t drinking enough on their own, whether during surgery, in the NICU or PICU, or on a general hospital ward, since it gives a fast bedside estimate without needing lab values or complex nomograms. It remains the standard teaching formula in medical and nursing education for maintenance fluids, distinct from resuscitation or replacement fluid calculations, which use different rules entirely.

This calculator takes a patient’s body weight and applies the 4-2-1 rule to return both the hourly maintenance fluid rate and the total daily volume.