A woman with grey hair, seen from behind, standing in low morning sun at the edge of a wood
Built on SURMOUNT-1 and STEP 1 body composition data

The scale is going down. Find out what is leaving with it.

A quarter of the weight lost on tirzepatide in SURMOUNT-1 was lean tissue. On semaglutide, closer to four in ten.

Resistance sessions a week
FreeNo accountTwenty seconds

At this pace, by the time you reach goal weight

0-0lb
of lean mass, gone
lean fat

Two things move that number

Protein
Resistance training

This is what the trial data says to expect. It is not a measurement of you. The only way to know whether you are on that line or under it is to put a real number beside it every week.

The projection is only half of it.

The trials tell you what to expect. Your scale tells you what is happening. GLPcomp puts both on one chart, and watches the distance between them. Three weeks below the line is a signal, and nothing else in your week will give you one.

Expected and actual, on one chartThe line the trial data puts you on, and the line you are actually on. The gap is the whole point.
Protein to a real target1.2 to 1.6 g per kg, tracked for an appetite that has gone quiet.
A training floor, not a programmeTwo to three sessions a week. You already have enough to do.
Any reading that measuresA smart scale weekly, a DEXA when you have one. Either gives you something real to check the expectation against.
Weight this morning 186.4lb down 1.2 lb this week
Lean mass, against expected -2.3lb

The same twelve weeks, read two ways

Forty-seven pounds is the only number a scale can give you. It cannot tell you which forty-seven.

What the scale says
Total weight-47 lb
What is actually happening
Fat mass-35 lb
Lean mass-12 lb

Why almost nobody catches it in time

Nothing looks wrong on the way down. The difference shows up at goal weight, in the mirror, when putting it back is a rebuild rather than a hold.

25%
of weight lost on tirzepatide was lean tissue, SURMOUNT-1
40%
on semaglutide, the STEP 1 body-composition substudy
$150
what a DEXA scan costs to confirm it, afterwards

How it works

  1. Tell it where you areDrug, weight, goal, and a body fat percentage if you have one. That last field is what gives you a line to check against.
  2. Weigh in and log the weekA weight when you have one, protein as you eat, training with one tap. Own a smart scale? Import its export.
  3. Watch the gap, not the numberExpected sits against actual every week. Drifting below the line shows up while there is still time to do something about it.
$49.99
a year, when it opens
One DEXA scan costs $50 to $150 and tells you where you are, once.
  • Expected against actual, updated every week
  • Lean and fat history, with the gap called out
  • Protein target and logging
  • Shot log, sites, titration, reminders
  • Smart-scale readings and DEXA scans, trended
  • Export everything, delete everything, any time

Not open yet, and nothing is charged. The projection is free and always will be.

Questions people actually ask

Is this medical advice?

No, and it never will be. It tracks and it estimates. It will never tell you what dose to take, when to change one, or whether to stay on the medication. That is your prescriber's job and the boundary is deliberate.

Do I need a DEXA scan for this to work?

No, but you do need something that measures. A weight and a goal give you an expectation from the trial data. To find out whether you are actually on it, the app needs a body fat reading to compare against, and any smart scale will do. A DEXA is better. With neither, it can tell you what to expect and keep you honest about protein, and that is all it will claim to do.

How accurate is it?

It is an estimate from population trial data, shown as a range, with a confidence state that reflects how much it knows about you. It is not a measurement of your body. A DEXA scan measures. This projects, and it tells you which it is doing.

What happens when I come off the medication?

The product is organised around your body, not around the drug, so it follows you into maintenance instead of going dark. That is the whole reason it is not just a shot tracker.

Who can see my data?

You. It is scoped to your account, it is never sold, and there is a one-tap export and a one-tap delete. Details on the privacy page, written in plain words.

Is this affiliated with Lilly or Novo Nordisk?

No. Not affiliated, not endorsed, not connected. The drug names appear only to identify which medication you take.

I read that GLP-1s preserve muscle. Which is it?

Both readings exist and they are not measuring the same thing. Trials that scan with DEXA, including SURMOUNT-1 and the STEP 1 body-composition substudy, put lean mass at a quarter to four tenths of the weight lost. A 2026 real-world study of 486 people reported skeletal muscle largely preserved, but it used bioelectrical impedance rather than DEXA, and skeletal muscle is a smaller thing than lean mass, which also holds water, glycogen and organ tissue. This page is built on the DEXA trials and names them on every number. The method page sets out both, including the study that argues against this product.

Why should I trust a product nobody has heard of?

You should not, yet. That is why the projection is free and the method is published in full. Run it, check the trials it cites, and decide from that rather than from a testimonial.

Who else is treating this as real

This is not a fringe worry. It has money, trials and clinical guidance behind it.

Eli Lilly

The company that makes Zepbound is running phase 2 trials on a second drug, bimagrumab, whose job is to stop the lean-mass loss that comes with the first one. If the problem were not real, there would be no programme.

NCT05616013NCT06643728NCT06890611NCT05933499
118 trials

Interventional studies registered as recruiting or active on ClinicalTrials.gov for GLP-1 and muscle. Ninety-six more for GLP-1 and lean mass. Counted in September 2026, and you can run the same query yourself.

Run the query
1.2 to 1.6 g

Protein per kilo of body weight per day, alongside progressive resistance training, is what the 2026 clinical guidance names for holding lean mass on these drugs. Those are exactly the two levers your projection moves, and exactly what the app tracks week to week.

The guidanceHow this is applied

It takes about twenty seconds. You already have the five numbers.