GLP-1 Goal Weight Calculator

How much do you have to lose to reach a healthy BMI?

There is one line of arithmetic behind this, and it is independent of height: the loss needed to reach the top of the healthy band is 1 − (24.9 ÷ your starting BMI). Written out:

Now read it against what the trials actually produced. The mean loss in the best arm of the largest tirzepatide obesity trial was 20.9%, and 14.9% in the semaglutide 2.4 mg trial. Against the table, that clears the healthy band from a starting BMI of about 31 on tirzepatide and about 29 on semaglutide — and those trials enrolled people averaging BMI 38.

Which means, plainly: for most people the healthy band is not the goal of this course of treatment. A goal weight set at a formula's number can be a target the medication was never going to hit — and that is a reason to set the target differently, not a reason to treat the result as a failure. The clinically meaningful thresholds sit far below the healthy band: 5–10% is where the health markers move. If the number stops moving well before you expected it to, that is its own problem with its own answers — what to do when Ozempic weight loss plateaus.

What the trials actually reached

One label to be scrupulous about: the "endpoint near BMI 30" figure is derived arithmetic on two numbers from the same publication — the mean baseline BMI and the mean percentage change — not a reported SURMOUNT-1 outcome. And all of these are means. SURMOUNT-1 reported that 94.5% of participants started at BMI 30 or above, and individual results spread widely either side of the average. If you want the shape of the loss over time rather than its endpoint, that is the 12-month GLP-1 weight-loss projection curve.

Ideal weight formulas: Devine, Robinson, Miller and Hamwi

The healthy-weight band at the top of this tool is arithmetic you can check: weight in kg equals BMI multiplied by your height in metres squared, worked at both ends of the 18.5–24.9 band. Everything else on the page is a formula — Devine, Robinson, Miller and Hamwi — and each one is just a base weight plus a fixed number of kilos for every inch above five feet. They differ only in the base and the increment, which is the entire reason they disagree with each other.

Two things jump out. The four formulas span about 7 lb at one height and 10 lb at the other, so no single one of them is the ideal weight. And they all sit low inside the healthy band: converted back to BMI, the female figures land around 21 and the male figures around 22 to 24, while the band itself runs to 24.9. Roughly the top quarter of a perfectly healthy weight range never appears in any formula output.

The trap: a single number that ignores what you are made of

None of these formulas take an input for body composition, because none of them have one. A powerlifter and a sedentary person of the same height and sex get the identical answer. That is not a rounding problem, it is the design: the formulas were built from small mid-twentieth-century datasets to produce a quick height-based estimate, and they carry no information about muscle, frame or fat distribution.

Which makes the output a reference point, not a clinical target. The tool cannot see your waist, your training history, or what your bloods look like, and it does not know why you are asking. A goal weight is something to set with your prescriber, who can weigh those things against the number.

What matters more once you are losing

When weight comes off, some of it is lean mass, and the honest figures are larger than most people expect. DXA sub-studies found about 26% of the weight lost on tirzepatide was lean tissue, and about 40% on semaglutide. The number that changes how you read those: the diet-and-exercise placebo group lost the same 25% share as lean. Lean loss is a property of losing weight, not something these medications do to you. The full comparison is in Zepbound vs Wegovy muscle loss.

Two caveats matter. DXA "lean mass" is not muscle — it includes organs and body water, both of which shrink as you get smaller. And when muscle was measured directly by MRI in a tirzepatide trial, the volume lost matched what would be predicted for that amount of weight loss, while fat infiltration within the muscle fell more than predicted. That is a better outcome than the DXA percentage alone implies.

The practical consequence is that the scale reaching a formula's number tells you nothing about the composition of the trip. Waist measurement, how your clothes fit, grip and general strength, and whether you are clearing a daily protein target for GLP-1 weight loss while training are all more informative than closing the last few pounds to a target. Put another way, the composition of the loss is a better goal than the endpoint number — which is also why a shot tracker that only logs weight misses body composition.

Where this tool does not apply

Under five feet, the formulas have no increment left to subtract — the tool floors the per-inch term at zero, so every height below 60 inches returns the same base weight. Treat those outputs as meaningless and use the BMI range instead. The BMI band itself is for adults, not children, who are assessed against age-and-sex growth charts, and it is not a guide in pregnancy.

BMI thresholds are also not applied identically everywhere: some national guidelines use lower cut-offs for particular ethnic groups, so confirm which band your clinician works to. And a high BMI carried as muscle is a well-known false positive. If the number looks wrong for your body, it probably is — that is the limitation of a formula with one input.

One more: this is not a prescribing threshold. Eligibility for these medications is set by BMI cut-offs plus comorbidities that vary by country and by payer, and a healthy-band goal has nothing to do with whether treatment is indicated. Nor does any of it replace the daily nutrition floors that make the loss survivable — the daily fibre target on a GLP-1 is the usual first gap once appetite drops.