Maintenance IV fluid calculator (4-2-1 rule)
A quick check of the maintenance fluid rate by weight, common in pediatrics and nursing.
Loading the tool…
Processing and privacy: The result is calculated inside your browser and your data is not sent to any server.
How to use it
- Enter weight.
- The result appears straight away and updates as you edit.
- Copy the result, or copy a link that keeps the same values to share it.
How it is calculated
Hourly (4-2-1): 4 mL/kg for the first 10 kg, 2 mL/kg for the next 10, and 1 mL/kg for each kg above 20. Daily (Holliday-Segar): 100 mL/kg for the first 10 kg, 50 for the next 10, and 20 for each kg above 20.
Example
Inputs: Weight = 25 kg. Result: Hourly rate (4-2-1): 65 mL/h; Daily total (Holliday-Segar): 1,600 mL/day.
Limits and caveats
- It covers maintenance only, not dehydration deficit or ongoing losses.
- It does not suit newborns and is restricted in heart and kidney disease.
- An educational estimate that does not replace assessment by a doctor or pharmacist.
Questions about this tool
Why is the daily total not the hourly rate × 24?
The 4-2-1 rule is an hourly approximation of the daily Holliday-Segar method, so they differ by a few mL.
Does it suit adults?
NICE guidance for adults suggests 25 to 30 mL/kg per day, often less than the rule gives at higher weights.
Where does the rule come from?
From the 1957 Holliday and Segar study that linked water needs to calories burned by weight.