GLP-1 weight loss calculator
For planning and record-keeping only — not medical advice. Your dose and schedule are set by your prescriber.
This calculator maps your current weight onto the average weight-loss curves from two pivotal trials — STEP 1 for semaglutide 2.4 mg and SURMOUNT-1 for tirzepatide 5, 10, and 15 mg. Pick a dose and a week from 4 to 72 to see what trial participants averaged at that point: a benchmark, not a prediction.
Trial participants averaged
body-weight change by week . Applied to , that trial mean works out to about — below the weight you entered.
An average is not a forecast. Roughly a third of participants in these trials lost noticeably more than the mean, and a meaningful share lost less. Participants with type 2 diabetes averaged smaller reductions in the companion trials, STEP 2 and SURMOUNT-2.
KeepAlong — GLP-1 shot tracker & planning tools
Once real weigh-ins start coming in, the number that matters is the gap between your data and this curve. The KeepAlong app reads weight from Apple Health and plots it against the trial mean — so you see where you actually stand relative to the study average, not where the average says you'd be.
The app is launching soon. The web tools on this site are free — no sign-up needed.
The trial data behind the numbers
This calculator runs on two placebo-controlled trials published in the New England Journal of Medicine — STEP 1 (Wilding et al., 2021) for semaglutide and SURMOUNT-1 (Jastreboff et al., 2022) for tirzepatide. Both enrolled adults with obesity or overweight and without diabetes (sources checked 2026-08-18). Every endpoint in the table below is a published trial mean; not every week in between is, and the method note under the table says which weeks are derived instead.
−20.9%
| Medication and dose | Mean weight change | Trial length | Source |
|---|---|---|---|
| Semaglutide 2.4 mg (Wegovy) | −14.9% (placebo −2.4%) | 68 weeks | STEP 1, NEJM 2021 |
| Tirzepatide 5 mg (Zepbound) | −15.0% (placebo −3.1%) | 72 weeks | SURMOUNT-1, NEJM 2022 |
| Tirzepatide 10 mg (Zepbound) | −19.5% (placebo −3.1%) | 72 weeks | SURMOUNT-1, NEJM 2022 |
| Tirzepatide 15 mg (Zepbound) | −20.9% (placebo −3.1%) | 72 weeks | SURMOUNT-1, NEJM 2022 |
The doses above are the maintenance doses from the FDA prescribing information for Wegovy(semaglutide 2.4 mg) and Zepbound (tirzepatide 5, 10, and 15 mg). Participants titrated up to those doses over the first 16–20 weeks, which is why every curve climbs slowly at first. Between the time points the papers report, this calculator interpolates linearly; past the final measurement — week 68 for semaglutide, week 72 for tirzepatide — it holds the mean flat. For tirzepatide 5 mg and 10 mg, only the week-72 endpoints — −15.0% and −19.5% — are taken from SURMOUNT-1: every earlier week on those two curves is the published 15 mg trajectory rescaled to end at that dose's own endpoint, not a value read from the paper.
What this calculator can't tell you
It can't turn an average into your outcome. A trial mean flattens enormous individual spread — response varies with biology, the dose you actually reach, titration speed, and adherence. The calendar matters too: trial participants climbed the dose ladder on a fixed schedule, and the titration schedule planner converts those label dose steps into dates, which is a better map of your first months than any average curve. It also can't rank medications for you — these were separate trials in separate populations, not a head-to-head comparison, and choosing between them is a prescribing conversation.
It also can't see how you weigh yourself. Day-to-day water shifts can exceed a whole week of average loss, so a single weigh-in against this curve means little — weighing under the same conditions each time is covered in what to track on GLP-1. If your question is syringe math rather than expectations, the units calculator handles the mg-to-units conversion. And comparing real weigh-ins against the trial curve week after week is a logging habit, not a calculation — that's the job of a GLP-1 shot tracker app.
Frequently asked questions
How much weight do people lose on semaglutide 2.4 mg?
In the STEP 1 trial, adults without diabetes taking semaglutide 2.4 mg averaged a 14.9% body-weight reduction at week 68, versus 2.4% on placebo. Applied to a 220 lb starting weight, that mean works out to roughly 33 lb — with wide individual spread on both sides of it.
How much weight will I lose on tirzepatide?
No calculator can answer that for an individual. In SURMOUNT-1, participants averaged 15.0% body-weight loss on 5 mg, 19.5% on 10 mg, and 20.9% on 15 mg at week 72. Your result depends on the dose you reach, titration speed, adherence, and biology — the trial mean is a benchmark, not a forecast.
What is the expected weight loss at 12 weeks on semaglutide?
STEP 1 participants on semaglutide 2.4 mg averaged roughly 6% body-weight loss by week 12; SURMOUNT-1 participants on tirzepatide’s highest dose averaged about 8%. Both trials were still titrating doses upward at that point, so 12-week numbers understate the eventual average — the curves keep falling well past week 20.
When is this calculator useless?
Whenever your situation differs from the trials behind it: type 2 diabetes (averages were lower in STEP 2 and SURMOUNT-2), a maintenance dose below the trial dose, compounded products, or frequent missed weeks. It also cannot rank medications, predict any individual outcome, or replace a conversation with your prescriber.
KeepAlong is an independent app and website. Not affiliated with, endorsed by, or sponsored by Novo Nordisk or Eli Lilly.