How the 4-2-1 rule works
The rule builds the hourly rate in three steps. Each of the first 10 kg earns 4 mL/h, each of the next 10 kg earns 2 mL/h, and each kg above 20 kg earns 1 mL/h. A 10 kg child therefore needs 40 mL/h, a 20 kg child 60 mL/h, and a child above 20 kg needs 60 mL/h plus 1 mL/h for each extra kg.
The daily volume is simply the hourly rate multiplied by 24. Rates are usually capped at 100 mL/h, which is 2.4 L a day, so larger adolescents do not receive adult-sized volumes by default.
Maintenance rate by weight
The table applies the hourly rule above, rounded to the nearest mL, with the 100 mL/h cap. Use it for a child who is not dehydrated and cannot drink, for example while nil by mouth around surgery or during an illness.
| Weight | Hourly rate | Daily volume |
|---|---|---|
| 3 kg | 12 mL/h | 288 mL/day |
| 5 kg | 20 mL/h | 480 mL/day |
| 10 kg | 40 mL/h | 960 mL/day |
| 15 kg | 50 mL/h | 1,200 mL/day |
| 20 kg | 60 mL/h | 1,440 mL/day |
| 30 kg | 70 mL/h | 1,680 mL/day |
| 40 kg | 80 mL/h | 1,920 mL/day |
| 50 kg | 90 mL/h | 2,160 mL/day |
| 70 kg | 100 mL/h (capped) | 2,400 mL/day |
Which fluid to use
The AAP recommends isotonic fluids with potassium and dextrose for children 28 days to 18 years, because hypotonic fluids raise the risk of hyponatremia. The calculator suggests 5% dextrose in 0.9% saline, lactated Ringer or Plasma-Lyte, with 20 mEq/L potassium chloride once the child is passing urine.
- Weigh daily and keep strict intake and output
- Check sodium, potassium and glucose at baseline and at least daily while on IV fluids
- Reduce the rate, often to two-thirds, in heart failure, kidney failure, edema or when SIADH is a risk (meningitis, pneumonia, brain injury, after surgery)
Newborns under 28 days
The AAP maintenance fluid guideline does not cover infants under 28 days, so the tool points to neonatal protocols instead. A typical term newborn starts at about 60 to 80 mL/kg/day of 10% dextrose on day 1, increasing by 10 to 20 mL/kg/day to 120 to 150 mL/kg/day by day 3 to 5, with sodium and potassium added after diuresis begins. Preterm infants follow the NICU's own protocol.
Assessing dehydration with the Clinical Dehydration Scale
Maintenance fluid alone is not enough for a dehydrated child. The Clinical Dehydration Scale scores four signs from 0 to 2 each: general appearance, eyes, mouth and tongue, and tears.
- Score 0: no dehydration; oral fluids at home
- Score 1 to 4: some dehydration, about 3 to 6%
- Score 5 to 8: moderate to severe dehydration, 6% or more
- Shock: weak pulses, cold limbs, slow capillary refill, low blood pressure or reduced consciousness
Rehydration plans
With some dehydration, oral rehydration works as well as IV for most children and is preferred: 50 mL/kg of oral rehydration solution over 4 hours if mild or 100 mL/kg if moderate, given as 5 mL every 1 to 2 minutes. Add 10 mL/kg for each watery stool and 2 mL/kg for each vomit. A single dose of oral ondansetron for children 6 months and older helps oral rehydration succeed.
If oral rehydration is not possible, give a 20 mL/kg bolus of 0.9% saline or lactated Ringer (maximum 1,000 mL) over 20 to 60 minutes. Estimate the deficit as about 5% of body weight, or about 8% when dehydration is moderate to severe. The hourly rate for the next 24 hours is the maintenance rate plus the deficit minus boluses, divided by 24. Correct over 48 hours if sodium is above 150 mmol/L, and change sodium no faster than 10 to 12 mmol/L per 24 hours.
In shock, give 10 to 20 mL/kg isotonic boluses over 5 to 20 minutes, reassessing after each, up to 40 to 60 mL/kg, and use 10 mL/kg boluses in heart disease or severe malnutrition.
Use the free tool
Maintenance rate, dehydration severity, oral rehydration and IV deficit replacement by weight.
Open IV Fluids & Dehydration →Common questions
What is the maintenance fluid rate for a 20 kg child?
By the 4-2-1 rule, 40 mL/h for the first 10 kg plus 20 mL/h for the next 10 kg gives 60 mL/h, or 1,440 mL a day.
Is there a maximum maintenance rate?
The tool uses a usual maximum of 100 mL/h, which is 2.4 L per day. Children above 60 kg reach this cap.
Why use isotonic fluid instead of hypotonic fluid?
The AAP 2018 guideline recommends isotonic fluids with potassium and dextrose for children 28 days to 18 years because hypotonic fluids raise the risk of hyponatremia.
Does the rule apply to newborns?
No. The AAP guideline covers 28 days to 18 years. Newborns follow neonatal fluid protocols, which start lower and increase over the first days of life.
Sources
Feld LG, Neuspiel DR, Foster BA, et al. Clinical practice guideline: maintenance intravenous fluids in children. Pediatrics 2018;142(6):e20183083.; Goldman RD, Friedman JN, Parkin PC. Validation of the Clinical Dehydration Scale. Pediatrics 2008;122:545-549.; Freedman SB, et al. Oral ondansetron for gastroenteritis. N Engl J Med 2006;354:1698-1705.; Holliday MA, Segar WE. Pediatrics 1957;19:823-832.
For education only, not medical advice. Always confirm against current guidelines and your local protocols. Pedemy is independent and not affiliated with or endorsed by the organizations cited.