Maintenance fluid calculator
Enter the weight, get the maintenance fluid rate.
What is the Holliday–Segar method?
A weight-based estimate of daily maintenance fluid from 1957: 100 mL per kg for the first 10 kg, 50 mL per kg for the next 10 kg, and 20 mL per kg for each kg above 20.
What is the 4-2-1 rule?
The hourly version: 4 mL/kg/h for the first 10 kg, 2 mL/kg/h for the next 10 kg, and 1 mL/kg/h above 20 kg.
Example
A 25 kg child: 1,000 + 500 + 100 = 1,600 mL a day (66.7 mL an hour). The 4-2-1 rule gives 40 + 20 + 5 = 65 mL an hour — slightly less, because the rules are rounded differently.
Does it apply to adults?
NICE guidance for adults on IV fluids uses a different approach and notes that men rarely need more than 2,500 mL and women more than 2,000 mL a day. The calculator shows a note above those amounts.
Is this a treatment plan?
No — fluid needs change with illness, losses, kidney function and other factors. Fluid orders come from a clinician.
Why do the daily and hourly methods give different numbers?
The 4-2-1 rule works out to 96, 48 and 24 mL per kg per day, while Holliday–Segar uses 100, 50 and 20. They differ because the hourly rule is rounded to whole mL per hour. The gap is small, a few percent.
What is the difference between maintenance, deficit and replacement?
Maintenance is the fluid a person normally needs to replace daily losses. Dehydration, ongoing losses such as vomiting or diarrhea, and other illness are separate, and a clinician adds them to the plan.
How the estimate is built
Both methods use weight in kilograms in three bands. The first 10 kg get 100 mL per kg per day (4 mL per hour), the next 10 kg get 50 mL (2 mL per hour), and every kilogram beyond 20 gets 20 mL (1 mL per hour). The bands add up: the total is not the weight times a single rate. The 1957 formula was built for children, which is why it is a pediatric tool; it does not account for fever, losses or disease.
Worked examples
For an 8 kg infant, all the weight is in the first band: 8 × 100 = 800 mL a day, 33.3 mL an hour; the 4-2-1 rule gives 32 mL an hour. For a 35 kg child: 1,000 + 500 + 15 × 20 = 1,800 mL a day, or 75.0 mL an hour, and the 4-2-1 rule gives 40 + 20 + 15 = 75 mL an hour; the two agree here. A weight of 55 lb is 24.9 kg.
Mistakes to avoid
Entering pounds as kilograms roughly doubles the estimate; divide pounds by 2.2046 first. Reading the hourly rate as a daily total, or the reverse, is the second slip: 65 mL an hour is 1,560 mL a day, not 65. Applying the pediatric bands to an adult gives amounts above those usually considered for adults, which is why the tool shows a note. Treat any figure here as a reference for learning and checking, not an order.
Sources: Holliday MA, Segar WE, "The maintenance need for water in parenteral fluid therapy," Pediatrics 1957; Merck Manual (maintenance fluids); NICE guideline NG29 (IV fluids for adults). Related tools: IV drip rate calculator, water intake calculator.
For general information only — not medical advice. Talk with your doctor or another health professional about your own health. How we check our calculators.