Adjusted Body Weight
Calculator

Adjusted body weight (AjBW) is a formula used mainly in clinical dosing when someone is obese, blending their ideal body weight with a fraction of the excess over ideal weight. It exists because using total body weight for dosing overestimates lean tissue, while using ideal weight alone underestimates it for people carrying more mass.

The standard formula adds 40% of the difference between actual and ideal weight to the ideal weight, because adipose tissue is metabolically active but not to the same degree as lean tissue. This 0.4 factor comes from pharmacokinetic studies and is a widely accepted clinical convention rather than a universal biological constant.

Adjusted body weight is typically used when actual weight exceeds ideal weight by more than about 20-30%, most often for dosing certain medications. If someone is at or near their ideal weight, actual weight and ideal weight are close enough that adjustment isn't needed.

No. This tool estimates a commonly used reference weight, but actual medication dosing must be verified against the specific drug's guidelines and a clinician's judgment. Treat the result as a starting reference, not a prescription.

The gap reflects how far your actual weight is from your calculated ideal weight; the further above ideal you are, the more the adjusted figure pulls away from your true scale weight. If you're near your ideal weight already, the two numbers will be nearly identical.