{ "slug": "adjusted-body-weight", "title": "Adjusted Body Weight Calculator", "heading": "Adjusted Body Weight Calculator", "category": "fitness-health", "url": "https://www.revenuelab.fyi/toolbox/adjusted-body-weight", "summary": "Dosing weight for obese patients that blends actual and ideal weight.", "description": "Adjusted body weight (AdjBW) is used for dosing certain medications in obese patients where neither actual body weight nor ideal body weight alone gives an accurate estimate of the effective volume of distribution. Actual weight overestimates dosing needs because fat has lower blood flow and drug affinity than lean tissue for many agents, while ideal body weight underestimates it because obese patients do carry more lean mass than a person at their \"ideal\" weight. The standard correction adds 40% of the excess weight above ideal body weight back onto the ideal weight, a factor derived from studies on drugs like aminoglycosides. This calculator is typically triggered when actual weight exceeds ideal weight by more than about 20-30%; below that threshold, most protocols simply use actual body weight. Not all drugs use this convention — check the specific medication's dosing reference, since some drugs (many chemotherapy agents, vancomycin loading doses) have their own obesity-dosing rules that differ from AdjBW. This tool is for education and workflow support only — not medical advice. Always verify results with a clinician and use clinical judgment alongside your institution's protocols.", "formula": "AdjBW = IBW + 0.4 × (Actual weight − IBW), used when actual weight is more than ~20-30% above IBW.", "dateModified": "2026-09-30", "run_url": "https://www.revenuelab.fyi/api/public/calc?tool=adjusted-body-weight", "inputs": [ { "id": "heightIn", "label": "Height", "kind": "number", "hint": null, "default": 66, "unit": "in", "min": 48, "max": 84 }, { "id": "sex", "label": "Sex", "kind": "select", "hint": null, "default": "female", "options": [ { "value": "male", "label": "Male" }, { "value": "female", "label": "Female" } ] }, { "id": "actualKg", "label": "Actual weight", "kind": "number", "hint": null, "default": 110, "unit": "kg", "min": 20, "max": 300 }, { "id": "factor", "label": "Correction factor", "kind": "number", "hint": null, "default": 0.4, "unit": null, "min": 0.1, "max": 0.5 } ], "outputs": [ { "id": "adjBW", "label": "Adjusted body weight", "format": "decimal", "hint": null, "primary": true }, { "id": "ibw", "label": "Ideal body weight", "format": "decimal", "hint": null, "primary": false }, { "id": "pctOver", "label": "% over IBW", "format": "decimal", "hint": null, "primary": false }, { "id": "recommend", "label": "Suggested approach", "format": "raw", "hint": null, "primary": false } ], "worked_example": { "inputs": [ "Height: 66 in", "Sex: Female", "Actual weight: 110 kg", "Correction factor: 0.4" ], "outputs": [ "Adjusted body weight: 79.6", "Ideal body weight: 59.3", "% over IBW: 85", "Suggested approach: Use adjusted body weight for applicable drugs" ] }, "how_to": { "title": "How to use this", "steps": [ "Enter height (in).", "Enter sex.", "Enter actual weight (kg).", "Enter correction factor.", "Read your adjusted body weight on the right — it updates as you type.", "Hit Share to keep the scenario or send it to someone." ] }, "scenarios": [ { "name": "Conservative", "description": "Lower-end numbers — what if things land soft?", "values": { "heightIn": 48, "sex": "female", "actualKg": 66, "factor": 0.24 } }, { "name": "Typical", "description": "Defaults — the most common real-world setup.", "values": { "heightIn": 66, "sex": "female", "actualKg": 110, "factor": 0.4 } }, { "name": "Ambitious", "description": "Higher-end numbers — what if things really pop?", "values": { "heightIn": 84, "sex": "female", "actualKg": 176, "factor": 0.5 } } ], "limitations": [ "Population formulas describe averages; individual bodies vary, especially at the extremes of height, age, or muscle mass.", "Results do not account for medical conditions, medication, or pregnancy.", "Use this as a directional reference, not a diagnosis — talk to a clinician before acting on it." ], "faq": [ { "q": "When should I use adjusted body weight instead of actual weight?", "a": "Most protocols reserve AdjBW for patients whose actual weight exceeds ideal body weight by roughly 20-30% or more. Below that, actual weight and IBW are close enough that using actual weight directly is standard for most medications." }, { "q": "Why 0.4 as the correction factor?", "a": "The 0.4 factor comes from pharmacokinetic studies, mainly on aminoglycoside antibiotics, showing that about 40% of a patient's excess weight above ideal behaves like lean tissue for volume-of-distribution purposes. It is an empirical average, not a universal constant, and some drug-specific guidelines use different factors." }, { "q": "Does this apply to all medications?", "a": "No. AdjBW is a convention for specific hydrophilic drugs with dosing historically studied this way — aminoglycosides being the classic example. Many drugs use actual body weight, ideal body weight, or a fixed dose regardless of weight, and some, like many chemotherapy regimens, use body surface area instead. Always check the specific drug's dosing guidance." }, { "q": "What if the patient's actual weight is below their IBW?", "a": "Then adjusted body weight is not applicable — use actual body weight, since the correction formula assumes excess weight above ideal, not a deficit. This calculator floors actual weight at IBW to avoid a nonsensical negative-excess result." } ], "related": [ "https://www.revenuelab.fyi/toolbox/ideal-body-weight", "https://www.revenuelab.fyi/toolbox/creatinine-clearance-cockcroft-gault", "https://www.revenuelab.fyi/toolbox/total-daily-insulin-dose" ], "license": "CC-BY-4.0", "citation": "RevenueLab — Adjusted Body Weight Calculator (https://www.revenuelab.fyi/toolbox/adjusted-body-weight)" }