What Is the Holliday-Segar Formula?
The Holliday-Segar formula is a clinical method for estimating daily fluid maintenance requirements based on body weight. It was originally developed for calculating intravenous fluid maintenance, especially in pediatric medicine, and remains a standard clinical reference today.
The Formula
First 10 kg of body weight: 100 ml/kg
Next 10 kg (10–20 kg): + 50 ml/kg
Every kg above 20 kg: + 20 ml/kg
Unlike a simple flat multiplier, this formula applies a different rate at each weight band — smaller bodies get proportionally more fluid per kilogram than larger ones, which reflects how metabolic and fluid needs scale with body size.
Worked Example: 70 kg Adult
| Weight Band | Calculation | Subtotal |
|---|---|---|
| First 10 kg | 10 × 100 ml | 1,000 ml |
| Next 10 kg (10–20 kg) | 10 × 50 ml | 500 ml |
| Remaining 50 kg (20–70 kg) | 50 × 20 ml | 1,000 ml |
| Total | 2,500 ml/day |
For a 70 kg adult, the Holliday-Segar formula estimates roughly 2.5 litres/day — a baseline maintenance figure, not adjusted for exercise, climate, or illness.
Holliday-Segar vs the General Adult Guideline
| Formula | Basis | Adjustable For | Typical Use |
|---|---|---|---|
| General guideline (33 ml/kg) | Flat rate per kg | Activity, climate, pregnancy/breastfeeding | Everyday personal hydration planning |
| Holliday-Segar | Tiered rate by weight band | Not built-in — clinical judgement applied separately | Clinical fluid maintenance dosing |
Both give a broadly similar ballpark for a typical adult, but they're built for different purposes. The general guideline is designed to be adjusted for your lifestyle and environment day to day. Holliday-Segar is a clinical baseline, historically used by healthcare providers to calculate maintenance fluid rates — it doesn't have activity or climate adjustments baked in.
Important: Holliday-Segar is shown here for reference and educational comparison, not as a replacement for personalised medical or clinical guidance. Actual clinical fluid dosing accounts for many additional factors a general calculator cannot.
Why We Show Both
Seeing two independently derived formulas land in a similar range builds confidence that neither number is arbitrary. Our Liquid Intake Calculator uses the general adult guideline as the primary, adjustable result, with the Holliday-Segar formula shown alongside as a clinical cross-check.