Paediatric fluid maintenance calculator

Malcolm Holliday and William Segar described this method in 1957, relating a child's water requirement to estimated energy expenditure. It is usually applied as an hourly rate — sometimes called 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 (10–20 kg), and 1 ml/kg/hr for each kg above 20 kg. Multiplying the hourly total by 24 gives the equivalent daily volume, which is the same formula expressed as 100 ml/kg/day, 50 ml/kg/day, and 20 ml/kg/day for the same three bands.

Each weight band is calculated separately and then added together, rather than applying a single rate to the whole body weight. For example, a 25 kg child draws the first 10 kg from the 4 ml/kg/hr band, the next 10 kg from the 2 ml/kg/hr band, and the remaining 5 kg from the 1 ml/kg/hr band — this calculator shows each contribution in the breakdown table above.

The Holliday-Segar formula estimates maintenance requirements only — the normal, ongoing fluid needs of a well child at rest. It does not account for pre-existing fluid deficit, ongoing abnormal losses (for example vomiting, diarrhoea, or surgical drains), fever, or conditions that alter fluid balance such as renal or cardiac disease, and it was derived from data on hospitalised children rather than validated across every clinical setting. This tool is for reference only and is not a substitute for clinical judgement — fluid type, rate, and any adjustment to these figures remain a decision for the treating clinician using local protocols.