Maintenance Fluids Calculator (4-2-1)
Hourly pediatric maintenance fluid rate by the 4-2-1 rule
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Maintenance Fluids Calculator (4-2-1) turns the numbers behind hourly pediatric maintenance fluid rate by the 4-2-1 rule into a result, step by step. Type Weight (kg) into Maintenance Fluids Calculator (4-2-1); each keystroke re-runs the math. In Maintenance Fluids Calculator (4-2-1) the working sits beside the answer. Anyone comparing options in Health can use Maintenance Fluids Calculator (4-2-1) to compare scenarios. Maintenance Fluids Calculator (4-2-1) is privacy-first: Health inputs stay offline. Maintenance Fluids Calculator (4-2-1) is part of the Health collection on CalcProMaster, alongside maintenance fluids calculator 4-2-1 rule pediatric hourly rate, free online maintenance fluids calculator (4-2-1) and more. Maintenance Fluids Calculator (4-2-1) is great for comparing scenarios. Change one value and watch. No sign-up or email — Maintenance Fluids Calculator (4-2-1) answers as you type.
What the defaults give
A 25 kg child needs 65 mL per hour of maintenance fluid by the 4-2-1 rule.
The rule is piecewise, not a single rate: 4 mL/kg/hr for the first 10 kg, 2 mL/kg/hr for the next 10, and 1 mL/kg/hr for every kilogram above 20. The rate per kilo falls as weight rises, which is the point.
The rule, piece by piece
First 10 kg → 4 mL/kg/hr = 40 mL/hr
Next 10 kg → 2 mL/kg/hr = 20 mL/hr
Each kg above 20 → 1 mL/kg/hr = 5 mL/hr for the remaining 5 kg
Total: 40 + 20 + 5 = 65 mL/hr.
Worked examples across weights
10 kg → 40 mL/hr
15 kg → 40 + 10 = 50 mL/hr
20 kg → 40 + 20 = 60 mL/hr
25 kg → 65 mL/hr
40 kg → 40 + 20 + 20 = 80 mL/hr
Where the numbers come from
The 4-2-1 rates are a simplification of the Holliday-Segar calculation, which estimates daily requirements as 100 mL/kg for the first 10 kg, 50 mL/kg for the next 10 and 20 mL/kg thereafter, divided by 24 hours. The two give the same hourly answer, which is why either is acceptable.
What maintenance fluid is not
- Not resuscitation. A dehydrated child needs a bolus based on clinical assessment, not the maintenance rate.
- Not a replacement for losses. Ongoing vomiting, diarrhoea or drainage has to be measured and replaced on top.
- Not fixed. Fever, burns, phototherapy and a hot environment raise requirements; cardiac or renal impairment lowers them.
- Not free water. The fluid composition matters — isotonic maintenance fluids are now preferred in most paediatric settings to avoid hyponatraemia.
Adults and the ceiling
The same arithmetic applies above 20 kg but quickly becomes an underestimate of adult needs. Most adult protocols cap maintenance fluid around 2,000–2,500 mL a day, which the 4-2-1 formula would exceed at high body weights.
Frequently Asked Questions
Why does a 25 kg child need 65 mL/hr?
40 mL/hr for the first 10 kg, 20 for the next 10, and 1 mL/kg/hr for the 5 kg above 20 — 40 + 20 + 5 = 65.
What is the 4-2-1 rule?
4 mL/kg/hr for the first 10 kg, 2 mL/kg/hr for the second 10 kg, and 1 mL/kg/hr for each kilogram above 20. It estimates hourly maintenance fluid.
Is 4-2-1 the same as Holliday-Segar?
Effectively yes. Holliday-Segar gives 100/50/20 mL per kg per day for the same weight bands; divided by 24 hours, that is the 4-2-1 rate.
Does fever change the rate?
Yes — requirements rise roughly 10–12% per °C above normal. The rule of thumb is to add 12% per degree, or use the 4-2-1 figure as a baseline and adjust clinically.
Should I use this for adults?
It gives a starting point, but most adult protocols cap maintenance at about 2,000–2,500 mL/day, which this formula exceeds at higher weights. Use the local adult guideline instead.
How much fluid is that in a day?
Multiply the hourly rate by 24: 65 mL/hr is about 1,560 mL a day, or 1.56 litres. The 100/50/20 mL/kg/day version gives the same total — 1,000 + 500 + 100 = 1,600 mL for a 25 kg child, with rounding explaining the small difference.
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