Adjusted body weight calculator
Adjusted body weight for dosing in obesity, from ideal and actual weight.
Use the factor the drug reference specifies.
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This is a reference implementation of a published formula, provided for use by qualified healthcare professionals. It does not diagnose, does not account for the individual circumstances of any patient, and is not a recommendation for treatment. Confirm every result against your own institutional guidance before acting on it. Clinical judgement always takes precedence over a calculator.
About this calculation
Where a drug distributes partly into adipose tissue, dosing on actual weight overshoots and dosing on ideal weight undershoots. Adjusted body weight adds back a fraction of the excess — conventionally 40%.
Formula
AdjBW = IBW + 0.4 × (actual weight − IBW)
- Source
- Widely used dosing convention; the 0.4 factor varies by agent
- Methodology version
- 1.0.0
- Last reviewed
- 2026-10-28
What this does not account for
- The 0.4 correction factor is a convention, not a constant. Aminoglycosides commonly use 0.4; other agents specify 0.3 or 0.5, and some should be dosed on actual or ideal weight instead.
- Adjusted body weight is only meaningful when actual weight exceeds ideal weight.
- Always check the dosing reference for the specific drug before applying this.