Last updated: 2026-06-21

Maintenance Fluids

Maintenance fluids are the water and electrolytes a person needs over a normal day to replace ordinary losses through urine, breathing, sweat, and stool. When someone cannot drink enough, this requirement guides intravenous fluid orders. This calculator applies the Holliday-Segar method for the daily volume and the 4-2-1 rule for the hourly rate.

The Holliday-Segar tiers

The daily requirement is built up in weight tiers:

• First 10 kg: 100 mL per kg.
• Next 10 kg (10–20 kg): 50 mL per kg.
• Each kg above 20 kg: 20 mL per kg.

The tiers taper because smaller bodies have a higher surface-area-to-mass ratio and lose proportionally more water.

The 4-2-1 hourly rule

The bedside infusion rate uses the same structure divided through to an hourly figure: 4 mL/kg/h for the first 10 kg, 2 mL/kg/h for the next 10 kg, and 1 mL/kg/h beyond 20 kg. Multiplying the hourly rate by 24 reproduces the daily estimate up to small rounding.

Worked example

For a 20 kg child the daily volume is the first two tiers in full:

The 4-2-1 rule gives $(10 \times 4) + (10 \times 2) = 60$ mL/h, which over 24 hours matches the 1500 mL daily figure.

Limitations

This covers routine maintenance only. It does not include an existing fluid deficit, ongoing losses from vomiting or drainage, fever, or conditions that demand fluid restriction such as heart or kidney failure. Those require separate replacement calculations. For general daily intake by mouth see the Daily Water Intake Calculator.