Rex says
Same equations the textbooks use — just way less awkward. Pop in your stats and I'll tell you what the number actually means for you.
Try a scenario
Click to load — tweak from there.Inputs
Result
Adjusted body weight
79.6
Ideal body weight
59.3
% over IBW
85
Suggested approach
Use adjusted body weight for applicable drugs
Psst — share this and help Rex grow
One click, a permanent link with your numbers baked in.
How to use this
- 1Enter height (in).
- 2Enter sex.
- 3Enter actual weight (kg).
- 4Enter correction factor.
- 5Read your adjusted body weight on the right — it updates as you type.
- 6Hit Share to keep the scenario or send it to someone.
About this calculator
Adjusted body weight (AdjBW) is used for dosing certain medications in obese patients where neither actual body weight nor ideal body weight alone gives an accurate estimate of the effective volume of distribution. Actual weight overestimates dosing needs because fat has lower blood flow and drug affinity than lean tissue for many agents, while ideal body weight underestimates it because obese patients do carry more lean mass than a person at their "ideal" weight. The standard correction adds 40% of the excess weight above ideal body weight back onto the ideal weight, a factor derived from studies on drugs like aminoglycosides. This calculator is typically triggered when actual weight exceeds ideal weight by more than about 20-30%; below that threshold, most protocols simply use actual body weight. Not all drugs use this convention — check the specific medication's dosing reference, since some drugs (many chemotherapy agents, vancomycin loading doses) have their own obesity-dosing rules that differ from AdjBW. This tool is for education and workflow support only — not medical advice. Always verify results with a clinician and use clinical judgment alongside your institution's protocols.
Worked example
Using the values the calculator loads with:
Inputs
- Height: 66 in
- Sex: Female
- Actual weight: 110 kg
- Correction factor: 0.4
Results
- Adjusted body weight: 79.6
- Ideal body weight: 59.3
- % over IBW: 85
- Suggested approach: Use adjusted body weight for applicable drugs
What each field means
Inputs
- Height (in)
- The height used in the calculation, measured in in. Starts at 66 in so you have a working example on load. Accepted range: 48–84 in.
- Sex
- Pick the option that matches your situation — the maths changes per option. Choices: Male, Female.
- Actual weight (kg)
- The actual weight used in the calculation, measured in kg. Starts at 110 kg so you have a working example on load. Accepted range: 20–300 kg.
- Correction factor
- The correction factor used in the calculation. Starts at 0.4 so you have a working example on load. Accepted range: 0.1–0.5.
Results
- Adjusted body weight
- Returned as a decimal number and shown as the headline result. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Ideal body weight
- Returned as a decimal number. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- % over IBW
- Returned as a decimal number. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Suggested approach
- Returned as a plain value. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
FAQ
When should I use adjusted body weight instead of actual weight?
Most protocols reserve AdjBW for patients whose actual weight exceeds ideal body weight by roughly 20-30% or more. Below that, actual weight and IBW are close enough that using actual weight directly is standard for most medications.
Why 0.4 as the correction factor?
The 0.4 factor comes from pharmacokinetic studies, mainly on aminoglycoside antibiotics, showing that about 40% of a patient's excess weight above ideal behaves like lean tissue for volume-of-distribution purposes. It is an empirical average, not a universal constant, and some drug-specific guidelines use different factors.
Does this apply to all medications?
No. AdjBW is a convention for specific hydrophilic drugs with dosing historically studied this way — aminoglycosides being the classic example. Many drugs use actual body weight, ideal body weight, or a fixed dose regardless of weight, and some, like many chemotherapy regimens, use body surface area instead. Always check the specific drug's dosing guidance.
What if the patient's actual weight is below their IBW?
Then adjusted body weight is not applicable — use actual body weight, since the correction formula assumes excess weight above ideal, not a deficit. This calculator floors actual weight at IBW to avoid a nonsensical negative-excess result.
Accuracy and limitations
- Population formulas describe averages; individual bodies vary, especially at the extremes of height, age, or muscle mass.
- Results do not account for medical conditions, medication, or pregnancy.
- Use this as a directional reference, not a diagnosis — talk to a clinician before acting on it.
Related tools
Ideal Body Weight Calculator (Devine Formula)
Devine formula IBW used for drug dosing and ventilator settings.
Creatinine Clearance Calculator (Cockcroft-Gault)
Estimate CrCl for drug dosing using the Cockcroft-Gault equation.
Total Daily Insulin Dose Estimator
Weight-based starting insulin dose split into basal and bolus components.
Cite this calculator
Writing about this topic? Grab a citation — every link helps keep these tools free.
RevenueLab. (2026). Adjusted Body Weight Calculator. Retrieved from https://www.revenuelab.fyi/toolbox/adjusted-body-weight
<p>Source: <a href="https://www.revenuelab.fyi/toolbox/adjusted-body-weight" target="_blank" rel="noopener">Adjusted Body Weight Calculator — RevenueLab</a> (2026).</p>
Source: [Adjusted Body Weight Calculator — RevenueLab](https://www.revenuelab.fyi/toolbox/adjusted-body-weight) (2026).