Maintenance fluid calculator (Holliday–Segar and adults)
Daily and hourly maintenance fluids for children (4-2-1 rule) and adults (25–30 mL/kg/day).
What this calculator is for
It works out routine maintenance fluid: the water a patient needs each day to replace normal urine, stool and insensible losses when they cannot drink. It is not for resuscitation and not for replacing abnormal losses.
Children: the Holliday–Segar (4-2-1) rule
- First 10 kg: 100 mL/kg/day (4 mL/kg/hour).
- Next 10 kg: 50 mL/kg/day (2 mL/kg/hour).
- Every kg above 20: 20 mL/kg/day (1 mL/kg/hour).
NICE NG29 recommends isotonic fluid (for example 0.9% saline or Ringer's lactate, with 5% dextrose added as needed) for routine maintenance in children. Hypotonic fluids such as 0.18% saline with 4% dextrose cause hospital-acquired hyponatraemia. Unwell children often secrete extra ADH, so many units restrict to about two-thirds of the calculated volume.
Adults (NICE CG174)
25–30 mL/kg/day of water, about 1 mmol/kg/day each of sodium, potassium and chloride, and 50–100 g/day of glucose to limit starvation ketosis. Use 20–25 mL/kg/day in older or frail patients and in heart or kidney failure. In obesity, base the volume on ideal body weight; adults rarely need more than 3 litres a day of maintenance.
Worked examples
A 25 kg child: 1000 + 500 + 100 = 1600 mL/day, about 65 mL/hour. A 60 kg adult: 1500–1800 mL/day, about 63–75 mL/hour.
Pitfalls
- Maintenance replaces normal losses only. Add replacement for vomiting, NG aspirate, diarrhoea, drains and fistulae separately, and measure them.
- Fever and hot wards increase insensible losses, so reassess in the Pakistani summer rather than adding a fixed amount.
- Shocked patients need boluses, not maintenance. Severely malnourished children follow the WHO malnutrition protocol.
- Check sodium, potassium and glucose at least daily while a patient is on IV fluids alone, and stop IV fluids as soon as they can drink.
- Use a weighed weight, not a guess, wherever possible.
See prescribing IV fluids, low sodium, diarrhoea and dehydration in children and the textbook chapter on IV fluids and electrolytes.
Frequently asked questions
What is the Holliday–Segar formula?
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 kg above 20 kg. The hourly version is the 4-2-1 rule.
How much maintenance fluid does a 70 kg adult need?
About 1.75–2.1 litres per day (25–30 mL/kg/day), less if frail or in heart or kidney failure.
Which fluid should I use for maintenance in children?
An isotonic fluid such as 0.9% saline or Ringer's lactate, with glucose added as needed, according to NICE NG29. Avoid hypotonic fluids such as 0.18% saline with 4% dextrose because of the risk of hyponatraemia.
Is maintenance fluid enough for a child with diarrhoea?
No. Maintenance covers normal losses only. Dehydration and ongoing stool losses need extra fluid, ideally as ORS by mouth using the WHO plans.
A calculator supports, but does not replace, clinical judgement. Check results before acting on them.