Health⏱ 5 min read
What Is Adjusted Body Weight and When Should You Use It?
Adjusted body weight (AjBW) corrects dosing and calorie calculations for obese patients — using actual weight overestimates needs, ideal weight underestimates them. Here's the formula.
When actual body weight significantly exceeds ideal body weight (IBW), using actual weight for calculations like calorie targets, medication dosing, and exercise prescriptions produces misleading results. Adjusted body weight provides a correction factor.
Ideal Body Weight (IBW) First
Devine Formula (most widely used):
Men: IBW (kg) = 50 + 2.3 x (Height in inches above 5 feet)
Women: IBW (kg) = 45.5 + 2.3 x (Height in inches above 5 feet)
Example: 178cm (5'10") man
Height above 5 feet: 10 inches
IBW = 50 + (2.3 x 10) = 50 + 23 = 73 kg
Example: 165cm (5'5") woman
Height above 5 feet: 5 inches
IBW = 45.5 + (2.3 x 5) = 45.5 + 11.5 = 57 kg
Converting cm to feet/inches: cm / 2.54 = inches total
Then: total inches / 12 = feet, remainder = extra inches
Adjusted Body Weight Formula
AjBW = IBW + 0.4 x (Actual weight - IBW)
The 0.4 factor accounts for the fact that excess adipose tissue
is not metabolically inert — it still needs some nutrition,
but proportionally less than lean tissue.
Example: 178cm man, actual weight 110 kg
IBW: 73 kg
Excess weight: 110 - 73 = 37 kg
AjBW = 73 + (0.4 x 37) = 73 + 14.8 = 87.8 kg
When to use AjBW vs IBW vs actual weight:
If actual weight < IBW: use actual weight
If actual weight 0-20% above IBW: use actual weight
If actual weight > 20% above IBW: use AjBW for most calculations
When AjBW Is Used
Calorie targets:
Clinical nutrition: calorie needs calculated from AjBW, not actual
Using actual weight overestimates by 20-40% in obesity
Protein targets in clinical settings:
1.2-2.0 g per kg AjBW (rather than actual weight)
Prevents overfeeding while ensuring adequate protein
Exercise prescription:
MET-based calorie calculations use actual body weight
(because you're literally moving that mass)
But VO2max estimations use lean body mass proxies
Drug dosing:
Many medications (particularly antibiotics and anaesthetics)
are dosed on AjBW or IBW — always follow clinical guidelines
rather than calculating independently for medications.
The 20% Rule in Practice
IBW: 73 kg
20% threshold: 73 x 1.20 = 87.6 kg
Actual weight 85 kg (below threshold): use actual weight (85 kg)
Actual weight 95 kg (above threshold): use AjBW
AjBW at 95 kg: 73 + 0.4 x (95-73) = 73 + 8.8 = 81.8 kg
Calorie target at 1.3 TDEE multiplier (lightly active):
Using actual 95 kg: ~2,600 kcal
Using AjBW 81.8 kg: ~2,240 kcal
Difference: 360 kcal/day — significant over time