Adjusted body weight = ideal body weight + 0.4 × (actual weight − ideal body weight). It is usually used when actual weight is more than about 120% of ideal body weight. Example: a 5′10″ man (IBW 73 kg) weighing 110 kg has an adjusted body weight of 73 + 0.4 × 37 = 87.8 kg.
Adjusted Body Weight Calculator
The adjusted body weight formula
IBW (women) = 45.5 + 2.3 × (height in inches − 60)
AjBW = IBW + 0.4 × (actual weight − IBW)
The 0.4 factor reflects that roughly 40% of excess weight is lean tissue and fluid that affects how some medicines distribute in the body. Some protocols use 0.3 or 0.25 for specific drugs.
When is adjusted body weight used?
- Dosing some antibiotics, such as aminoglycosides, in people with obesity.
- Estimating kidney function with the Cockcroft–Gault equation in some hospitals.
- Calculating energy and protein needs in clinical nutrition for people with a high BMI.
Do not use this calculator to change your own medicine doses. Always follow advice from your doctor, pharmacist or dietitian.
Worked example
A woman is 5′5″ (65 inches) and weighs 95 kg.
- IBW = 45.5 + 2.3 × 5 = 57.0 kg
- Actual is 167% of IBW, so adjusted weight is appropriate.
- AjBW = 57.0 + 0.4 × (95 − 57.0) = 57.0 + 15.2 = 72.2 kg
Frequently asked questions
What is adjusted body weight?
It is a weight between your ideal and actual weight, used by clinicians for some calculations when actual weight is much higher than ideal body weight.
When should adjusted body weight be used?
Commonly when actual body weight is more than 120% (sometimes 130%) of ideal body weight, depending on the medicine or calculation.
What is the difference between ideal and adjusted body weight?
Ideal body weight is based only on height and sex. Adjusted body weight also takes 40% of any excess weight into account.
Related tools and guides
About this page
How this tool works
Ideal body weight is calculated with the Devine formula (men 50 kg, women 45.5 kg, plus 2.3 kg per inch over 5 ft). Adjusted body weight adds 40% of the difference between actual and ideal weight. This tool is for education; prescribing must follow local clinical guidance.
Sources
- NHS – Calculate your body mass index (BMI) for adults
- Devine BJ. Gentamicin therapy. Drug Intell Clin Pharm 1974;8:650–655.
Medical disclaimer: this tool gives an estimate for adults and is not a diagnosis or medical advice. bmicalculatornhs.net is independent and not affiliated with the NHS. Speak to your GP, pharmacist or another qualified health professional about your own health. Full disclaimer.