How do you calculate paediatric maintenance fluids?
Split the child’s weight into three bands and give each band its own allowance. The first 10 kg count the most, the next 10 kg half as much, and every kilogram above 20 kg much less.
Hourly (4-2-1): 4 mL/kg/h × first 10 kg + 2 mL/kg/h × next 10 kg + 1 mL/kg/h × each kg above 20
Daily (100-50-20): 100 mL/kg × first 10 kg + 50 mL/kg × next 10 kg + 20 mL/kg × each kg above 20
The calculator also divides the daily volume by 24, so you can compare it directly with the 4-2-1 rate.
How to use the calculator
- Enter the child’s Weight in kg.
- Read the Hourly rate (4-2-1) in mL/h.
- Read the Daily volume (100-50-20) in mL/day and the Daily volume ÷ 24 in mL/h.
- Check the steps: each one shows what each weight band contributes.
Worked examples
Example 1 – 8 kg. All the weight is in the first band. Hourly: 8 × 4 = 32 mL/h. Daily: 8 × 100 = 800 mL/day, which is 33.3 mL/h.
Example 2 – 15 kg. 10 kg in the first band, 5 kg in the second. Hourly: 40 + (5 × 2) = 50 mL/h. Daily: 1,000 + (5 × 50) = 1,250 mL/day, which is 52.1 mL/h.
Example 3 – 28 kg. 10 kg, 10 kg, then 8 kg above 20. Hourly: 40 + 20 + (8 × 1) = 68 mL/h. Daily: 1,000 + 500 + (8 × 20) = 1,660 mL/day, which is 69.2 mL/h.
Maintenance fluids by weight
| Weight | 4-2-1 (mL/h) | 100-50-20 (mL/day) | Daily ÷ 24 (mL/h) |
|---|---|---|---|
| 3 kg | 12 | 300 | 12.5 |
| 5 kg | 20 | 500 | 20.8 |
| 10 kg | 40 | 1,000 | 41.7 |
| 15 kg | 50 | 1,250 | 52.1 |
| 20 kg | 60 | 1,500 | 62.5 |
| 25 kg | 65 | 1,600 | 66.7 |
| 30 kg | 70 | 1,700 | 70.8 |
| 40 kg | 80 | 1,900 | 79.2 |
| 50 kg | 90 | 2,100 | 87.5 |
Common mistakes
- Multiplying the whole weight by one figure. 4 mL/kg/h × 25 kg = 100 mL/h is wrong; the bands give 65 mL/h.
- Mixing the two rules. 4-2-1 is per hour, 100-50-20 is per day. Using 100 mL/kg as an hourly figure is a 24-fold error.
- Forgetting other fluids. IV drugs, flushes and feeds also count towards what the child receives. The fluid balance calculator helps you total them.
- Using an estimated weight when a measured one is available. Small children have small margins.
Limits of the method
The formulas estimate the needs of a well child at rest. Acutely unwell children may retain water, and NICE NG29 describes giving less than full maintenance in that situation; deficits and ongoing losses are added separately. The method is not meant for term neonates. For children with obesity, local protocols may say which weight to use; the guide to actual, ideal and adjusted body weight explains the options. In burns, maintenance is added to the Parkland formula volume. The result is best treated as a starting point to check against the prescription.
Frequently asked questions
What is the 4-2-1 rule?
It gives an hourly maintenance rate: 4 mL/kg/h for the first 10 kg, 2 mL/kg/h for the next 10 kg and 1 mL/kg/h for every kg above 20. For a 15 kg child that is 40 + 10 = 50 mL/h. It is the hourly form of the Holliday-Segar daily method.
What is the 100-50-20 (Holliday-Segar) rule?
It gives a daily volume: 100 mL/kg for the first 10 kg, 50 mL/kg for the next 10 kg and 20 mL/kg for every kg above 20. For a 15 kg child that is 1,000 + 250 = 1,250 mL per day. Divided by 24, that is 52.1 mL/h.
Why do the two methods give slightly different hourly rates?
Because the 4-2-1 rule is a rounded hourly version of the daily formula. For 10 kg, 4-2-1 gives 40 mL/h while 1,000 mL ÷ 24 is 41.7 mL/h. The gap stays small at every weight. The calculator shows both, so you can see the difference; it’s best to use the one your protocol names.
Where does the method come from?
Holliday and Segar published it in 1957. They linked the water needs of hospitalised children to their energy expenditure: about 100 mL of water for every 100 kcal used. The weight bands reflect how energy use per kilogram falls as a child grows.
Can it be used for newborns?
Not as it stands. Term neonates in their first weeks of life have their own fluid requirements, based on day of life, and guidance such as NICE NG29 treats them separately. Below 5 kg the calculator shows a reminder that newborns in their first weeks follow different rules.
Why is there a warning for heavier children?
Because above 2,000 mL a day the result reaches the volumes NICE NG29 treats as the usual ceiling: over 24 hours, females rarely need more than 2,000 mL and males more than 2,500 mL. With the 100-50-20 rule, the daily volume passes 2,000 mL above 45 kg.
Does maintenance include losses or deficits?
No. Maintenance covers normal daily needs only. Replacement of ongoing losses, such as vomiting or diarrhoea, and correction of dehydration are calculated separately and added on top. Acutely unwell children may also need less than full maintenance, as described in NICE NG29.