Adjusted Body Weight Calculator
Calculate adjusted body weight (AdjBW) from ideal body weight and actual weight, used for medication dosing in obesity
By Waqar Mushtaq · Last updated:
Adjusted Body Weight (AdjBW) is a dosing weight used mainly in clinical settings for patients whose actual weight is well above their ideal body weight. Many medications don't distribute evenly into fat tissue, so dosing purely on actual weight can overshoot — AdjBW splits the difference between ideal and actual weight to better estimate a patient's lean, drug-distributing mass.
Adjusted Body Weight Formula
O(1) calculationDevine formula, male — height in inches, 60 in = 5 ft
Devine formula, female
Adjusted body weight, 40% adjustment factor
This calculator first finds Ideal Body Weight (IBW) using the Devine formula, then adjusts it toward actual weight using a 40% correction factor. Both weights come out in kilograms internally and are converted for display in your chosen unit system.
The 40% factor is the conventional value used for drug dosing and renal function (creatinine clearance) estimates. Some nutrition-focused calculations use a 25% factor instead — this calculator uses the 40% dosing convention since that's the more common use case, and is what the underlying formula was originally developed for.
Adjusted body weight is conventionally used instead of actual or ideal weight when actual weight exceeds roughly 120% of IBW — below that threshold, clinicians typically dose on actual or ideal weight directly, since the correction has little practical effect. The Devine formula itself is defined only for adult heights of 5 ft (152.4 cm) and above.
Use Cases
Medication dosing in obesity
Drugs like aminoglycoside antibiotics that distribute poorly into fat tissue are often dosed on AdjBW instead of actual weight, to avoid overdosing in patients well above their ideal weight.
Estimating renal function (creatinine clearance)
Some creatinine clearance equations (e.g. Cockcroft-Gault) call for an adjusted or ideal weight input rather than actual weight for patients above ideal weight, to avoid overestimating kidney function.
Comparing actual, ideal, and adjusted weight at a glance
The comparison bars show all three weights side by side, making it easy to see how far a patient's actual weight sits above ideal, and where the adjusted figure lands between the two.
Frequently Asked Questions
When should adjusted body weight be used instead of actual or ideal weight?
Conventionally, when actual weight is more than about 20% above ideal body weight (actual > 1.2 x IBW). Below that threshold, the difference between actual, ideal, and adjusted weight is small enough that many clinicians dose on actual or ideal weight directly.
Why is a 40% adjustment factor used instead of 100% (actual weight) or 0% (ideal weight)?
Excess body weight above ideal is mostly fat, and fat tissue is not metabolically or vascularly equivalent to lean tissue for most drug distribution. The 40% factor is an empirically-derived approximation of how much of that excess weight should count toward dosing weight — not a strict physiological ratio.
Does this replace medical judgment or a pharmacist's dosing calculation?
No. This calculator implements the standard Devine/adjusted body weight formulas for reference, but actual medication dosing should always be confirmed against a drug's specific dosing guidance and a clinician or pharmacist familiar with the patient.
Methodology
The formula above is implemented as a standalone module covered by unit tests, so its worked examples are re-checked on every change to the site. It is verified against the authoritative sources listed below.
Not medical advice. This calculator is a general informational tool and cannot account for your individual circumstances. See the terms of use.
Maintained by Waqar Mushtaq. Spotted a result that looks wrong? Report it and it becomes a failing test.