{"success":true,"version":"v1","request":{"tool":"get_calculator_schema","calculator_id":"maintenance-fluids"},"result":{"entity_type":"calculator","id":"maintenance-fluids","calculator_id":"maintenance-fluids","canonical_url":"https://tttkmbb.com/medical/maintenance-fluids","name":"Maintenance Fluids Calculator","title":"Maintenance IV Fluids Calculator – Holliday-Segar 4-2-1 Rule and 100-50-20 Daily Volume","category":"medical","category_name":"Medical & Clinical","tool_name":"calculate_maintenance_fluids","featured_mcp_tool":false,"description":"Calculates maintenance fluid requirements from body weight with the Holliday-Segar method: the hourly 4-2-1 rule and the daily 100-50-20 mL/kg volume, plus the NICE 25–30 mL/kg/day adult range.","use_when":"You need a baseline maintenance fluid rate for a child or adult who cannot take fluids orally.","do_not_use_when":"There are ongoing losses, dehydration, heart or kidney failure, or the patient is a neonate; those need individual assessment and the estimate is informational only.","inputs":[{"name":"weight_kg","label":"Weight","type":"number","unit":"kg","required":true,"min":1,"max":300,"description":"Body weight in kilograms.","example":25}],"outputs":[{"name":"hourly_rate_ml_per_h","label":"Hourly rate (4-2-1)","type":"number","unit":"mL/h","decimals":1,"description":"4 mL/kg/h for the first 10 kg, 2 for the next 10 kg, 1 for each kg above 20."},{"name":"daily_volume_ml","label":"Daily volume (100-50-20)","type":"number","unit":"mL/day","decimals":0,"description":"100 mL/kg for the first 10 kg, 50 for the next 10 kg, 20 for each kg above 20."},{"name":"daily_from_hourly_ml","label":"Hourly rate × 24","type":"number","unit":"mL/day","decimals":0,"description":"The 4-2-1 rule extrapolated to a day (slightly below the 100-50-20 volume)."},{"name":"nice_adult_min_ml_per_day","label":"NICE adult range (min, 25 mL/kg)","type":"number","unit":"mL/day","decimals":0,"description":"25 mL/kg/day, the lower bound NICE CG174 recommends for adults; only reported for weights of 40 kg or more."},{"name":"nice_adult_max_ml_per_day","label":"NICE adult range (max, 30 mL/kg)","type":"number","unit":"mL/day","decimals":0,"description":"30 mL/kg/day, the upper bound for adults; only reported for weights of 40 kg or more."}],"input_schema":{"type":"object","properties":{"weight_kg":{"description":"Body weight in kilograms. Unit: kg.","type":"number","minimum":1,"maximum":300,"examples":[25],"x-unit":"kg"}},"additionalProperties":false,"required":["weight_kg"]},"output_schema":{"type":"object","properties":{"hourly_rate_ml_per_h":{"description":"4 mL/kg/h for the first 10 kg, 2 for the next 10 kg, 1 for each kg above 20. Unit: mL/h.","type":"number","x-unit":"mL/h"},"daily_volume_ml":{"description":"100 mL/kg for the first 10 kg, 50 for the next 10 kg, 20 for each kg above 20. Unit: mL/day.","type":"number","x-unit":"mL/day"},"daily_from_hourly_ml":{"description":"The 4-2-1 rule extrapolated to a day (slightly below the 100-50-20 volume). Unit: mL/day.","type":"number","x-unit":"mL/day"},"nice_adult_min_ml_per_day":{"description":"25 mL/kg/day, the lower bound NICE CG174 recommends for adults; only reported for weights of 40 kg or more. Unit: mL/day.","type":"number","x-unit":"mL/day"},"nice_adult_max_ml_per_day":{"description":"30 mL/kg/day, the upper bound for adults; only reported for weights of 40 kg or more. Unit: mL/day.","type":"number","x-unit":"mL/day"}}},"formula":"hourly = 4 × min(W, 10) + 2 × min(max(W − 10, 0), 10) + 1 × max(W − 20, 0); daily = 100 × min(W, 10) + 50 × min(max(W − 10, 0), 10) + 20 × max(W − 20, 0); W = weight_kg","method":"Holliday and Segar (1957) linked water needs to caloric expenditure (1 mL per kcal); the 4-2-1 rule is the bedside approximation of the daily formula, and adults usually receive less (NICE: 25–30 mL/kg/day) because the rule over-predicts at high weights. Results are informational only and not a substitute for clinical judgement or medical advice.","sources":[{"name":"Holliday MA, Segar WE (1957) The maintenance need for water in parenteral fluid therapy, Pediatrics 19:823-832","url":"https://pubmed.ncbi.nlm.nih.gov/13431307/","type":"peer_reviewed","retrieved_at":"2026-09-24"},{"name":"NICE CG174 (2013, updated 2017) Intravenous fluid therapy in adults in hospital","url":"https://www.nice.org.uk/guidance/cg174","type":"standard","retrieved_at":"2026-09-24"}],"freshness":{"type":"static","max_age_seconds":null,"note":"Deterministic formula with fixed constants; results never go stale. Inputs supplied by the caller determine the output."},"examples":[{"name":"25 kg child","inputs":{"weight_kg":25},"expected":{"hourly_rate_ml_per_h":65,"daily_volume_ml":1600,"daily_from_hourly_ml":1560},"url":"https://tttkmbb.com/api/v1/calculate/maintenance-fluids?weight_kg=25"},{"name":"70 kg adult","inputs":{"weight_kg":70},"expected":{"hourly_rate_ml_per_h":110,"daily_volume_ml":2500,"nice_adult_min_ml_per_day":1750,"nice_adult_max_ml_per_day":2100},"url":"https://tttkmbb.com/api/v1/calculate/maintenance-fluids?weight_kg=70"}],"faq":[{"q":"Why do the hourly and daily results disagree?","a":"100 mL/kg/day is 4.17 mL/kg/h; the 4-2-1 rule rounds this down, so hourly × 24 is about 2–3% below the daily formula."},{"q":"Which fluid should be used?","a":"The method gives volume only. Current paediatric guidance favours isotonic fluids with glucose; the choice of fluid and electrolytes is a clinical decision."}],"tags":["maintenance fluids","holliday segar","4-2-1 rule","iv fluids","pediatric fluids"],"related":[{"calculator_id":"parkland-formula","reason":"Burn resuscitation volume on top of maintenance."},{"calculator_id":"iv-drip-rate","reason":"Convert the hourly rate into a drip rate."},{"calculator_id":"water-intake","reason":"Oral fluid guidance for healthy adults."}],"links":{"html":"https://tttkmbb.com/medical/maintenance-fluids","markdown":"https://tttkmbb.com/medical/maintenance-fluids.md","json":"https://tttkmbb.com/medical/maintenance-fluids.json","api":"https://tttkmbb.com/api/v1/calculate/maintenance-fluids","schema":"https://tttkmbb.com/api/v1/calculators/maintenance-fluids","openapi":"https://tttkmbb.com/openapi.json","mcp":"https://tttkmbb.com/mcp"},"version":"v1","updated_at":"2026-09-24"},"timestamp":"2026-09-24T01:48:08Z"}