TBWL (Total Body Weight Loss)

TBWL stands for Total Body Weight Loss, expressed as a percentage of your starting weight. It is the standard currency of obesity medicine: trials report it, clinicians think in it, and coverage criteria are often written in it. Fifteen percent TBWL for someone starting at 200 pounds is 30 pounds.

It is used instead of raw pounds because pounds are not comparable across people. Thirty pounds is a transformation for someone at 200 and a rounding error for someone at 400. Percentage loss scales, which makes trial arms comparable and makes thresholds meaningful.

Those thresholds are where the term earns its keep. Around 5% TBWL, blood pressure, triglycerides and blood sugar measurably improve. Around 10%, sleep apnea and fatty liver typically respond. Around 15% and above, diabetes remission becomes a realistic possibility for some people. This is why trials report the proportion reaching each threshold rather than only the average: in STEP 1, 86.4% reached 5%, 69.1% reached 10% and 50.5% reached 15%; in SURMOUNT-1 at 15 mg, 91% reached 5% and 57% reached 20%.

The confusion worth correcting is treating the trial average as your forecast. STEP 1’s 14.9% and SURMOUNT-1’s 20.9% are group means with wide spreads underneath them, measured in supported trial populations at maintenance doses reached after months of escalation. Roughly one in seven people on semaglutide in STEP 1 did not reach even 5%.

A second confusion: TBWL is not the same as excess weight loss, the measure often quoted after bariatric surgery, which is calculated against the weight above an ideal — a different denominator producing a much larger-sounding number.

Ask your clinician what percentage would meaningfully change your specific health risks, and by when they expect to judge whether the drug is working. Our weight-loss calculator and BMI calculator convert percentages into your own numbers.