Maintenance IV Fluids Calculator
Holliday-Segar daily maintenance fluids and the 4-2-1 hourly rule by weight, with an optional two-thirds restriction.
What it does
Maintenance fluids replace what a patient would normally drink, breathe out, and pass as urine, when they cannot take fluids by mouth. The standard recipe for children and young people comes from Holliday and Segar: a weight-based daily volume split into three bands.
The first 10 kg count at 100 mL/kg/day, the next 10 kg at 50 mL/kg/day, and every kilogram above 20 at 20 mL/kg/day. A 10 kg child therefore needs about 1,000 mL per day, and a 25 kg child about 1,600 mL.
Running the same idea by the hour gives the 4-2-1 rule: 4 mL/kg/hr for the first 10 kg, 2 mL/kg/hr for the next 10, and 1 mL/kg/hr beyond 20. For the 10 kg child that is 40 mL/hr, a number many wards use as their starting pump setting.
The two views are close but not identical: 1,000 mL spread over 24 hours is 41.7 mL/hr, a little more than 40. The gap is why units pick one convention and document it. NICE also gives practical ceilings, 2,500 mL per day in males and 2,000 in females, because the formula keeps scaling after real needs flatten.
When antidiuretic hormone runs high, for example after surgery, NICE advises considering 50% to 80% of routine maintenance. This page shows both the full rate and a two-thirds version so you can see the range.
How to use
- Pick kilograms or pounds to match the chart you are reading from.
- Enter the body weight; pounds convert to kilograms for the formula.
- Choose full maintenance, or the two-thirds restriction when water retention is a risk.
- Read the daily volume in mL per day.
- Compare the two hourly figures: the daily formula divided by 24, and the 4-2-1 rule.
- Check the ceilings in the notes, confirm the fluid type and electrolytes with the local protocol, and prescribe with a clinician.
Formula
- kg
- Body weight in kilograms; pounds divide by 2.2046.
- First 10 kg
- The first 10 kg of weight carry the highest rate in both rules.
- Ceiling
- About 2,500 mL/day in males and 2,000 mL/day in females, per NICE.
The daily formula and the 4-2-1 rule come from the same bands, so they stay close at every weight: the daily version runs slightly higher because dividing by 24 smooths the hourly steps. NICE NG29 states the ceilings (males rarely need more than 2,500 mL, females more than 2,000 mL) and, when water retention from ADH is a risk, suggests restricting to 50% to 80% of the calculated routine needs. Two-thirds sits inside that band and is a common ward shorthand.
Worked example
Example: 10 kg child, full maintenance
10 kg, no restriction (defaults).
- First 10 kg: 10 x 100 = 1,000 mL/day.
- No kilograms above 10, so nothing more to add.
- Daily formula divided by 24: 1,000 / 24 = 41.7 mL/hr.
- 4-2-1 rule: 10 x 4 = 40 mL/hr.
- Both point to roughly 40 mL/hr; confirm fluid type and electrolytes with the local protocol.
Reference table
| Weight | Daily (Holliday-Segar) | Hourly (4-2-1) |
|---|---|---|
| 5 kg | 500 mL | 20 mL/hr |
| 10 kg | 1,000 mL | 40 mL/hr |
| 20 kg | 1,500 mL | 60 mL/hr |
| 30 kg | 1,700 mL | 70 mL/hr |
| 40 kg | 1,900 mL | 80 mL/hr |
| 50 kg | 2,100 mL | 90 mL/hr |
Limits
- Maintenance only. Resuscitation boluses and deficit replacement are different calculations.
- Term neonates have their own day-by-day schedule; from day 1 the guide runs 50 to 60 mL/kg/day upward, not the flat Holliday-Segar bands.
- The formula gives volume, not composition. Sodium, potassium, and glucose come from lab values and local protocols.
- Fever, burns, drains, and other ongoing losses need extra replacement on top of maintenance.
Common mistakes
- Using the 4-2-1 figure and the daily divided-by-24 figure as if they must match exactly.
- Skipping the NICE ceilings, so a 90 kg adult is prescribed the full formula output.
- Forgetting febrile illness raises maintenance needs slightly while ADH states lower them.
- Confusing maintenance with deficit replacement after vomiting or diarrhea.
- Scaling the restriction percentage at the wrong level, or applying it without a documented reason.
Try it yourself
Quick checks. Answers sit tucked under each question.
A 25 kg child, full maintenance?
1,000 + 500 + 5 x 20 = 1,600 mL/day; 4-2-1 gives 40 + 20 + 5 = 65 mL/hr.
An 8 kg infant, full maintenance?
8 x 100 = 800 mL/day; 4-2-1 gives 32 mL/hr.
A 20 kg child at two-thirds?
1,500 x 2/3 = 1,000 mL/day; 4-2-1 becomes 60 x 2/3 = 40 mL/hr.
Questions
When are maintenance fluids used?
When a child cannot drink enough: before and after surgery, during illness with poor intake, or when oral fluids are paused. They replace normal losses but not extra ones.
Why is there a ceiling on the daily volume?
The bands keep adding volume for every kilogram, but real needs flatten in heavier patients, and excess fluid can cause swelling and low sodium. NICE gives the practical ceilings.
Is 4-2-1 the same as Holliday-Segar?
They come from the same bands. 4-2-1 is the hourly form used for pump rates; Holliday-Segar is the daily form. They differ slightly because 24 hours does not divide the steps evenly.
What about newborns?
Term neonates follow a day-based schedule that starts near 50 to 60 mL/kg/day and rises over the first week. Use the neonatal schedule, not the flat bands.
Which fluid is used?
NICE recommends isotonic crystalloids with sodium in the range 131 to 154 mmol/L for routine maintenance, with glucose added for term neonates 8 days and over. The exact bag is set by the local protocol.
How does the restriction work?
When water retention from ADH is a risk, NICE suggests either 50% to 80% of routine maintenance or a calculation from insensible losses. Two-thirds is a common shorthand inside that band.
Sources
- NICE guideline NG29: intravenous fluid therapy in children and young people, routine maintenance
- Royal Children's Hospital Melbourne: intravenous fluids, maintenance table with the 4-2-1 column