The Holliday-Segar method is the standard formula for estimating a pediatric patient's baseline intravenous fluid needs from body weight alone. Published in 1957 and still taught and cited today, it gives clinicians two related figures: an hourly infusion rate for pump programming, and a 24-hour total for daily fluid balance. This calculator computes both directly from the original tiered formulas.
How the calculator works
The calculator applies two independent weight-tiered formulas from Holliday & Segar's 1957 paper. The hourly rate uses the '4-2-1 rule': 4 mL/kg/hr for the first 10 kg of body weight, 2 mL/kg/hr for the next 10 kg, and 1 mL/kg/hr for every kilogram above 20 kg. The daily total uses the '100-50-20 rule': 100 mL/kg/day for the first 10 kg, 50 mL/kg/day for the next 10 kg, and 20 mL/kg/day for every kilogram above 20 kg.
Both formulas are applied directly, not derived from one another. This matters because 4/2/1 mL/kg/hr multiplied by 24 hours works out to 96/48/24 mL/kg/day — close to, but not the same as, 100/50/20. The daily figures are independently rounded clinical constants from the same original paper, and the calculator's Daily Total tab explains this discrepancy with your own live numbers so it doesn't read as an error.
Inputs and what they mean
Body weight is the only input this calculator needs, entered in kilograms or pounds. There is no age, sex, or clinical-status input, because the Holliday-Segar method itself is weight-only — it estimates maintenance needs from the relationship between body weight and metabolic rate, not from age or other patient characteristics.
Because the method is weight-only, it also does not adjust for dehydration, edema, or obesity. If a patient's actual weight diverges meaningfully from a healthy baseline for their build, many clinicians use an adjusted or ideal body weight rather than the number on the scale — that adjustment is a clinical judgment call this calculator does not make for you.
Limits and edge cases
Holliday-Segar was derived for pediatric patients and has no built-in upper limit — it keeps adding 20 mL/kg/day for every kilogram above 20 kg with no ceiling. At and above 60 kg, this calculator shows an advisory noting that many institutions cap adult maintenance fluids around 2,400 mL/day, and that large, obese, or adult patients need clinical adjustment rather than a literal application of the pediatric formula.
The formula also does not account for renal, cardiac, or hepatic impairment, ongoing abnormal losses (fever, vomiting, diarrhea, burns, drains), electrolyte status, or any concurrent IV medications or fluids that must be added on top of the maintenance total. This is an educational reference calculation, not a fluid order — always verify against a prescriber's order or facility protocol before administering any IV fluid.