Tool

Weight-Loss Percentage Calculator

All calculations show inputs, formula, date and disclaimer

Why percentage rather than pounds

Clinical trials report weight change as a percentage of starting weight, because a fixed number of pounds means something different at different starting points. Converting your own figures to a percentage is what makes them comparable to published results.

For context on the scale involved: in SURMOUNT-1, mean reduction was about 15.0% at 5 mg, 19.5% at 10 mg and 20.9% at 15 mg over 72 weeks, against 3.1% with placebo. Those are group means in a trial population under structured supervision.

What a trial mean does not tell you

A 20.9% mean contains people who lost substantially more and people who lost very little. Trial populations meet specific eligibility criteria and receive structured support that most people do not have. An average describes what happened to a group; it does not predict what will happen to any individual, and it is not a target.

What this tool does with your numbers

Arithmetic, in your browser. Nothing is transmitted or stored. This is a conversion, not a clinical assessment, and any interpretation of your own numbers belongs in a conversation with a clinician.

Why trials report percentages, not pounds

Every figure in this field is a percentage of starting body weight: 22.5% at tirzepatide 15 mg in SURMOUNT-1, 13.7% for semaglutide 2.4 mg in the SURMOUNT-5 head-to-head, 14.0% regained after withdrawal in SURMOUNT-4.

The reason is comparability. A 20 lb loss means something different at 180 lb than at 320 lb, and a trial enrolling both needs one scale. Converting your own progress to a percentage is the only way to place it against published results.

The thresholds that carry meaning

5% is the conventional threshold at which metabolic benefits begin to appear in the literature, and it is the bar many coverage criteria use to judge whether treatment is working.

10% is where the evidence on obstructive sleep apnoea and joint pain becomes clearer. Beyond roughly that point, additional loss may not produce proportionally more benefit for every outcome — the knee osteoarthritis data suggest exactly that.

15% and above is the range the high-efficacy agents reach at maintenance doses over 72 weeks.

Comparing yourself to a trial figure, fairly

Three things make the comparison unfair if you skip them. Trial figures are means, and the distribution around them is wide. They are measured at 72 weeks, not at three months. And they are at a maintenance dose, which the label's titration schedule takes 20 to 24 weeks to reach.

If you are twelve weeks in and below the headline number, you are comparing a different point on a curve. Our first twelve weeks page sets out what that period actually is.

What the number cannot tell you

Whether the loss is fat or lean mass. Roughly 21% of weight lost on semaglutide was lean mass in the phase 2 work that added a myostatin inhibitor, which cut that share to about 7%. A scale cannot see the difference, and composition is the thing that determines function later.