Lesson overview
Pediatric Maintenance Fluid Calculations: 4-2-1 & 100-50-20
Ready when you are
Start with short teaching slides, then answer the lesson questions. Your progress stays on this browser.
Learning outcomes
What you will learn
- explain what a maintenance-fluid formula result represents in this maths lesson
- split a weight into the first 10 kg, next 10 kg and kilograms above 20
- calculate the 4-2-1 hourly estimate one band at a time
- calculate the 100-50-20 daily estimate one band at a time
- recognise which bands are used at 10 kg, 20 kg and weights above 20 kg
- keep the hourly and daily methods separate instead of forcing them to match, while recognising that they can occasionally coincide at a particular weight
- recognise that the arithmetic result does not by itself choose a real clinical fluid plan
- separate maintenance volume from IV-fluid composition and understand the modern isotonic-maintenance boundary in the population covered by current guidance
- recognise that reduced maintenance and large-child maximums are guideline-specific clinical adjustments rather than extra MedMaths formulas
- use the current authorised kilogram weight basis without letting a unit conversion silently choose the clinical weight method
- recognise that the formula does not decide whether IV therapy is needed and that oral or enteral hydration may be preferred when clinically appropriate
- account for reassessment, total fluid exposure and fluid creep while keeping display precision separate from prescribing or pump precision
Clinical connection
Why this matters
A common arithmetic mistake is applying one band's rate to the whole weight. A separate clinical mistake is treating a mathematically correct full-maintenance estimate as the whole fluid prescription. This lesson teaches both boundaries explicitly.
Quick concept
Split the weight into bands before applying either maintenance-fluid method
Both methods use the first 10 kg, next 10 kg and kilograms above 20 kg as separate bands. The 4-2-1 shortcut estimates an hourly mL/hr value, while the 100-50-20 Holliday-Segar method estimates a daily mL/day value. Calculate each band separately and add the results.
Formula
4-2-1: 4 / 2 / 1 mL/kg/hr; 100-50-20: 100 / 50 / 20 mL/kg/day across the same three weight bands
Worked example
Educational example: a fictional maintenance-fluid exercise gives a verified weight of 25 kg.
4-2-1 = 40 + 20 + 5 = 65 mL/hr; 100-50-20 = 1000 + 500 + 100 = 1600 mL/day
Answer: 65 mL/hr by 4-2-1 and 1600 mL/day by 100-50-20
These formulas estimate standard full-maintenance volume; they do not decide whether IV fluid is needed, which fluid or additives to use, how to account for deficit or ongoing losses, or whether a child requires restriction or another patient-specific plan.
Lesson plan
How the lesson works
- 1
Learn
Short teaching slides explain one idea at a time with plain-language examples.
- 2
Practise
Answer calculation or scenario questions and receive immediate feedback.
- 3
Finish
Complete the lesson check and save your learning progress on this browser.
Keep going
Learn, practise, apply and check this skill
Use the page that matches what you need next. Each resource has a different job, so the lesson can stay focused on teaching the skill.
Practise
Pediatric maintenance fluid practice questions
Practise 4-2-1, 100-50-20, weight-band boundaries and method-comparison questions across four levels.
Understand
Paediatric maintenance fluids explained
Review why 4-2-1 and 100-50-20 are related but not exact 24-hour conversions, plus clinical limitations.
Check
Pediatric Maintenance Fluids Calculator
Calculate hourly and daily maintenance estimates from a verified weight within the calculator's stated scope.
Apply
Paediatric calculation cases
Use pediatric fluid arithmetic and weight-based calculations inside evolving clinical scenarios.