CalcVitalsAdjusted Body Weight Calculator
Adjusted body weight sits between ideal and actual weight: ideal body weight plus 40% of the excess. For example, a man of 175 cm weighing 100 kg has an adjusted body weight of about 82.3 kg (ideal 70.5 kg + 0.4 × 29.5 kg).
How it works
Some drug doses and nutrition prescriptions scale with body weight, but in obesity the full actual weight overstates the body's needs — fat tissue takes up drug and burns energy at lower rates than lean tissue — while ideal body weight understates them, because a larger body genuinely carries more lean mass too. Adjusted body weight is the profession's compromise between the two.
The standard construction takes the Devine ideal body weight and adds a correction factor — most commonly 0.4 — times the excess of actual over ideal. The factor is not sacred: institutions use values between 0.25 and 0.4 depending on the drug and the evidence behind it, which is why the formula is printed here in full and why the treating team, who know their protocol, always has the final word.
You will meet this number in hospital nutrition plans, renal dosing and some anaesthetic calculations. If a document quotes your 'dosing weight' and it matches neither your scale weight nor your ideal weight, this page is almost certainly why.
The method
Adjusted BW = IBW + 0.4 × (actual BW − IBW), with IBW from the Devine formula (men 50 kg + 2.3 kg/inch over 5 ft; women 45.5 kg + 2.3 kg/inch). The 0.4 correction factor is the most common convention; some protocols use 0.25–0.3.
Frequently asked questions
Why not just use actual body weight for dosing?
For many drugs you can — and clinicians do. Adjusted weight is reserved for medicines whose distribution into fat is limited, where full actual weight would overdose and ideal weight would underdose. The choice is drug-specific and belongs to the prescriber.
Why is the factor 0.4?
It is an empirical compromise fitted to observed drug behaviour in obesity — roughly, excess weight behaves as if about 40% of it were lean tissue for distribution purposes. Some institutions standardise on 0.25 or 0.3 instead.
My adjusted weight is lower than my ideal weight. Is that right?
That happens when actual weight is below ideal weight. In that situation adjusted weight is simply not the convention — actual or ideal weight is used — so ignore the figure in that case.