What maintenance fluids are
Maintenance fluids replace the water a person loses every day through urine, breathing, sweat and stool when they cannot drink normally, for example during an illness or after surgery. In 1957, Holliday and Segar linked daily water needs to calorie use, which led to two simple weight-based rules still taught in pediatrics: the 100/50/20 rule per day and the 4-2-1 rule per hour.
The rules
| Body weight | Per day (100/50/20) | Per hour (4-2-1) |
|---|---|---|
| First 10 kg | 100 mL/kg | 4 mL/kg/h |
| Next 10 kg (11 to 20 kg) | 50 mL/kg | 2 mL/kg/h |
| Each kg above 20 kg | 20 mL/kg | 1 mL/kg/h |
The calculator converts pounds to kilograms automatically (1 kg = 2.2046 lb).
Worked example
A child weighs 44 lb, which is almost exactly 20 kg.
- Hourly rate: 10 × 4 + 10 × 2 = 40 + 20 = 60 mL/h.
- Daily volume: 10 × 100 + 10 × 50 = 1,000 + 500 = 1,500 mL/day (1,498 mL for 19.96 kg).
- Rate × 24 h = 1,440 mL, a little less than the daily rule.
The two rules give slightly different totals because the hourly rule is a rounded version of the daily one. Both are acceptable starting points.
For an adult of 70 kg, the 4-2-1 rule gives 40 + 20 + 50 = 110 mL/h, and the daily rule gives 1,500 + 50 × 20 = 2,500 mL.
What the rules do not cover
- Dehydration deficit: a child who has lost 5% of body weight needs that volume replaced on top of maintenance.
- Ongoing losses: vomiting, diarrhea, drains, fever and burns increase needs.
- Reduced needs: heart failure, kidney failure, some brain conditions and the risk of excess antidiuretic hormone after surgery call for less fluid.
Which fluid
Current pediatric guidelines, including the 2018 American Academy of Pediatrics guideline, recommend isotonic fluids with potassium and dextrose for most children who need maintenance IV fluids, because hypotonic fluids increase the risk of low blood sodium. Many adult protocols use 25 to 30 mL/kg/day and cap the rate around 100 to 120 mL/h.
Weigh children accurately, monitor urine output and electrolytes, and reassess the rate at least daily.
This calculator is for general information and education. It is not medical advice and does not replace the judgment of a doctor, nurse or pharmacist who knows the full clinical picture.