The Holliday-Segar Fluid Maintenance Calculator estimates how much intravenous fluid a patient needs over 24 hours simply to replace normal ongoing losses (urine, sweat, breathing, and stool). It uses the classic Holliday-Segar method, most commonly remembered as the 4-2-1 rule for hourly rates.
How it works
The method scales fluid to body weight in three tiers. The hourly (4-2-1) form:
- 4 mL/kg/h for the first 10 kg
- 2 mL/kg/h for the next 10 kg (from 10 to 20 kg)
- 1 mL/kg/h for each kg above 20 kg
The three contributions are summed. The equivalent daily (100-50-20) form uses 100 mL/kg, 50 mL/kg, and 20 mL/kg over the same weight tiers; dividing the daily total by 24 reproduces the hourly figure.
For a 25 kg child:
(10 × 4) + (10 × 2) + (5 × 1) = 40 + 20 + 5 = 65 mL/h, or about1560 mL/day.
Tips and notes
This figure is a maintenance baseline only. Add separately for replacement of any existing deficit (dehydration) and for ongoing abnormal losses such as vomiting, diarrhoea, or surgical drains. Fever raises insensible losses by roughly 10–12% per degree Celsius above normal.
In larger adults the weight-scaled rate is usually capped (often near 100–120 mL/h) and individualised, because linear scaling overestimates needs at high body weights. Always reassess fluid status clinically and with electrolytes rather than relying on the formula alone.
Reference values at common weight milestones
For quick clinical reference, here are the Holliday-Segar maintenance rates at common paediatric weight milestones:
| Weight | Hourly rate | Daily total |
|---|---|---|
| 5 kg | 20 mL/h | 500 mL/day |
| 10 kg | 40 mL/h | 1000 mL/day |
| 15 kg | 50 mL/h | 1250 mL/day |
| 20 kg | 60 mL/h | 1500 mL/day |
| 25 kg | 65 mL/h | 1560 mL/day |
| 30 kg | 70 mL/h | 1700 mL/day |
| 40 kg | 80 mL/h | 1900 mL/day |
| 70 kg | 110 mL/h | 2600 mL/day (often capped in practice) |
When to adjust above the maintenance baseline
The Holliday-Segar formula gives the floor, not the ceiling. Several clinical situations require a higher total fluid input:
Dehydration — the deficit is estimated from the degree of dehydration (mild ≈ 5% body weight, moderate ≈ 10%, severe ≈ 15%) and added to the maintenance total, typically replacing half over the first 8 hours and the rest over 16 hours.
Ongoing losses — active vomiting, diarrhoea, nasogastric drainage, surgical wound outputs, or high-output ostomies must each be measured and replaced volume-for-volume with a fluid of appropriate electrolyte composition.
Fever — each degree Celsius above normal increases insensible losses by roughly 10–12%. A child at 39 °C (2 degrees above normal) may need roughly 20–24% more than the baseline maintenance.
Burns — paediatric burns follow dedicated fluid resuscitation protocols (such as Parkland or modified Galveston) that are separate from and much larger than Holliday-Segar maintenance.
When to reduce below maintenance
Certain conditions require fluid restriction rather than free maintenance fluids:
- SIADH (syndrome of inappropriate ADH secretion) — causes water retention; fluid restriction is a primary treatment.
- Oliguria post-surgery — replace only measured losses plus insensible losses rather than running full maintenance.
- Cardiac or renal failure — strict fluid balance targets may mandate rates well below the formula output.
Always assess the clinical picture, urine output, and electrolytes alongside any calculated rate.
Medical disclaimer: This tool is for educational and reference purposes. All fluid prescriptions must be reviewed and ordered by a qualified clinician who can assess the individual patient’s status.