Maintenance Fluid Calculator (Holliday–Segar 4-2-1 Rule)

Maintenance fluid calculator using the Holliday–Segar and 4-2-1 rules

For healthcare professionals and students. Check results against your local protocols and clinical judgement; this tool does not give medical advice.

This maintenance fluid calculator works out routine maintenance water by body weight. For children and young people it uses the Holliday–Segar daily rule (100, 50 and 20 mL/kg/day) and the bedside 4-2-1 rule for an hourly rate, side by side, so you can see why they differ by a few mL/h. For adults it also shows the NICE CG174 starting range of 25–30 mL/kg/day, or 20–25 mL/kg/day for older, frail or at-risk patients.

It adds the checks that guidelines attach to the numbers — the NICE NG29 daily ceilings, neonatal rates, fluid restriction and the adult obesity note — and it never chooses the fluid for you. Everything runs in your browser.

How to use the Maintenance Fluid Calculator

1. Choose Holliday–Segar / 4-2-1 or NICE adults.
2. Enter the body weight in kg or lb.
3. For children, optionally choose the sex to check the NICE daily ceiling, and enter a percentage only if your protocol restricts fluids.
4. For adults, tick the box if the patient is older or frail, has renal impairment or cardiac failure, or is malnourished.
5. Read the hourly and daily volumes and the working, then the notes underneath.

Maintenance Fluid Calculator features

The Holliday–Segar formula and the 4-2-1 rule

Holliday MA and Segar WE, Pediatrics 1957;19(5):823–832, linked water needs to energy expenditure — about 100 mL of water for every 100 kcal used — and expressed it by weight: 100 mL/kg/day for the first 10 kg, 50 mL/kg/day for the next 10 kg and 20 mL/kg/day for each kg above 20. Dividing by 24 and rounding gives the hourly 4-2-1 rule: 4 mL/kg/h, 2 mL/kg/h and 1 mL/kg/h.

Hand-calculated example: a 25 kg child needs 1,000 + 500 + 100 = 1,600 mL/day (66.7 mL/h); by 4-2-1 it is 40 + 20 + 5 = 65 mL/h (1,560 mL/day). The small gap is the rounding of 4.17 to 4.

What NICE says (children and adults)

For children and young people, NICE guideline NG29 (last updated 11 June 2020) recommends calculating routine maintenance with the Holliday–Segar formula, notes that over 24 hours males rarely need more than 2,500 mL and females more than 2,000 mL, recommends isotonic crystalloids containing 131–154 mmol/L sodium for initial maintenance, and suggests considering 50–80% of routine maintenance when there is a risk of water retention from non-osmotic ADH secretion. Term neonates have their own day-by-day rates.

For adults, NICE CG174 (last updated 5 May 2017) restricts the initial routine maintenance prescription to 25–30 mL/kg/day of water with about 1 mmol/kg/day of potassium, sodium and chloride and 50–100 g/day of glucose; suggests 20–25 mL/kg/day for older or frail patients, those with renal impairment or cardiac failure and those at risk of refeeding syndrome; and for obese patients uses ideal body weight — the ideal weight calculator can help. Both pages checked 19 October 2026.

What maintenance does not cover

• Resuscitation boluses, existing deficits (dehydration) and ongoing losses such as vomiting, diarrhoea or drains are calculated separately.
• Burns need a resuscitation formula; see the Parkland formula calculator.
• Electrolytes and glucose must be checked when maintenance fluids start and at least daily, as NICE NG29 recommends.
• Weight-based formulas overestimate needs in obesity and in conditions with water retention.