Weight loss on a GLP-1 medicine is slow, then steady, then flat — and the trial averages say so plainly. In the STEP-1 trial, people on semaglutide lost about 15% of their starting weight by 68 weeks; in SURMOUNT-1, people on tirzepatide lost about 20%, and in the 2025 head-to-head SURMOUNT-5 trial tirzepatide reached 20.2% versus 13.7% for semaglutide at 72 weeks. This tool turns those trial averages into a week-by-week curve for your starting weight — so you can see what "average" really looks like, month by month, instead of guessing from a single headline number. It gives no dosage advice, and it promises nothing: these are averages across trial participants, and your own result will differ. For your protein target while losing weight, see our GLP-1 protein calculator.
Expect the biggest drops in months 3 to 9, smaller drops after that, and a near-plateau by about 15 to 17 months. A 200 lb person on the semaglutide trial average would be around 190 lb at 12 weeks, 180 lb at 28 weeks, and 170 lb at 68 weeks. A 220 lb person on the tirzepatide trial average would be around 204.6 lb at 12 weeks, 189.2 lb at 28 weeks, and 175.6 lb at 72 weeks. Those are trial averages, not predictions for you.
| Week | Average loss | Lost so far | Weight |
|---|
These figures are trial averages interpolated between published trial time points. They are not a promise, a prediction, or medical advice for you. Actual results vary widely with dose tolerance, diet, activity, sleep, and whether treatment continues.
Every number this tool produces is a trial average: the mean result across hundreds or thousands of trial participants, many of whom lost more and many of whom lost less. That distinction is the whole point of the tool. A headline that says "20% weight loss" describes a group, not a person, and it hides the spread that matters to you — some participants lost far less, some stopped early because of side effects, and some regained weight after the trial ended. If your own curve runs below the average, that does not mean the treatment has failed; if it runs above it, that does not mean it will keep going at the same rate. The curve also flattens for a physiological reason: as you lose weight, your body needs fewer calories, your appetite hormones adjust, and the same dose produces a smaller weekly deficit than it did at a higher weight. Plateaus are therefore a normal part of the average curve, not a sign that something has gone wrong.
The two medicines in this tool are not interchangeable, and the tool does not rank them for you. Semaglutide's best-known result comes from STEP-1, where participants lost about 15% of body weight by 68 weeks on the weekly dose studied, alongside lifestyle support. Tirzepatide's comes from SURMOUNT-1 at about 20% and from the head-to-head SURMOUNT-5 trial in 2025, where tirzepatide reached 20.2% versus 13.7% for semaglutide at 72 weeks in the same trial population. The head-to-head number is the fairest comparison between the two drugs, and it is smaller than the gap between the two separate trials suggests — a reminder that comparing results across different trials, with different participants and different support, always exaggerates differences. Your clinician, not this tool, decides which medicine, if any, fits your health history, and this tool gives no dosage information at all: doses are titrated by clinicians over weeks and months, and the timeline here assumes the trial dosing schedule was followed, which is itself an idealization.
The average curve has three phases, and knowing them in advance prevents the most common disappointment. In the first month, losses are modest — about 2% on the semaglutide average and about 3% on the tirzepatide average by week 4 — because doses are still being increased and appetite suppression is still building. This is the phase where people most often conclude the medicine "isn't working," when in fact the trial average says a slow start is normal. Months 2 to 9 are the steep phase: by week 12 the averages reach about 5% (semaglutide) and 7% (tirzepatide), and by week 28 about 10% and 14%. That is roughly 1 to 2 lb a week for a 200 lb person in the middle of the curve — fast enough to notice in clothes and energy, slow enough to be mostly fat rather than muscle, provided protein and resistance training keep pace. After about a year, the curve bends: week 52 sits at about 13% and 18%, and the final trial points — 15% at week 68 and 20.2% at week 72 — add only a little more. The last months of the trial are mostly maintenance of a new, lower weight, not continued rapid loss.
| Trial-average point | Semaglutide (STEP-1) | Tirzepatide (SURMOUNT) |
|---|---|---|
| Week 4 | ~2% | ~3% |
| Week 12 | ~5% | ~7% |
| Week 28 | ~10% | ~14% |
| Week 52 | ~13% | ~18% |
| Final trial point | ~15% at 68 weeks | ~20.2% at 72 weeks |
A note on honesty about the intermediate points: the trials published their headline endpoints and selected interim results, not a weekly measurement for every week. The points between endpoints in this tool are straight-line interpolations between published anchors, labelled as such, so the curve is smooth where real life is bumpy. Real weeks include holidays, illness, dose changes, and stalls of two or three weeks with no movement at all — none of which appear in an average curve. Judge your progress by the trend across a month, not by any single week's weigh-in, and weigh under consistent conditions (same time of day, same scale, after using the bathroom) so that water shifts do not masquerade as fat changes.
Every number below comes straight from the tool's anchors, so you can verify them by hand. Percentage loss times starting weight gives pounds lost; starting weight minus pounds lost gives the new weight. All figures are rounded to one decimal place.
| Example | Week 12 | Week 28 | Final point |
|---|---|---|---|
| 200 lb, semaglutide | 5% = 10 lb lost, 190 lb | 10% = 20 lb lost, 180 lb | 15% = 30 lb lost, 170 lb at 68 weeks |
| 220 lb, tirzepatide | 7% = 15.4 lb lost, 204.6 lb | 14% = 30.8 lb lost, 189.2 lb | 20.2% = 44.4 lb lost, 175.6 lb at 72 weeks |
| 180 lb, semaglutide | 5% = 9 lb lost, 171 lb | 10% = 18 lb lost, 162 lb | 15% = 27 lb lost, 153 lb at 68 weeks |
Take the 220 lb tirzepatide example step by step. At 12 weeks, 7% of 220 lb is 15.4 lb, so 220 minus 15.4 is 204.6 lb. At 28 weeks, 14% of 220 is 30.8 lb, so 220 minus 30.8 is 189.2 lb. At 72 weeks, 20.2% of 220 is 44.44 lb, rounded to 44.4, so 220 minus 44.4 is 175.6 lb. The semaglutide example works the same way: 15% of 200 lb is exactly 30 lb, so the final trial-average weight is 170 lb. Notice how the weekly pace slows: the 200 lb semaglutide example loses 10 lb in the first 12 weeks, another 10 lb in the next 16 weeks, and only 4 lb in the final 16 weeks. That deceleration is the normal shape of the curve, not a failure of willpower or of the medicine.
This is the part of the timeline most people never see in an advertisement, and it is the reason the tool includes a stopping mode. In withdrawal studies, people who stopped treatment regained a large share of the weight they had lost — on the order of two-thirds within about a year after stopping in the STEP-1 extension, with appetite returning and weight climbing steadily rather than all at once. The tool's stopping illustration uses that pattern conservatively: it assumes about one-third of the loss is kept a year after stopping, and two-thirds returns. For the 200 lb semaglutide example, that means a trial-average low of 170 lb, then a climb back toward about 190 lb twelve months after stopping (170 plus two-thirds of the 30 lb lost, which is 20 lb). That is an illustration of a study pattern, not a prediction for any individual, and it varies enormously with what replaces the medicine — continued dietary habits, activity, sleep, and in some cases a maintenance plan agreed with a clinician.
The practical lesson is not that stopping is forbidden — people stop for cost, side effects, pregnancy plans, or personal choice, and those are legitimate reasons to discuss with a clinician — but that the plan after stopping deserves as much attention as the plan during treatment. The habits that protect the loss are unglamorous and well-evidenced: keep protein high (our GLP-1 protein calculator sets a target range), keep resistance training in the week at least twice, keep weighing weekly so a 5 lb regain is caught before it becomes 20 lb, and keep the food environment that made the loss possible rather than reverting to the one that preceded it. If cost is the reason for stopping, that conversation belongs with your clinician and pharmacist, who may know about support programs or alternative plans; it does not belong in a calculator, and this page offers no advice on it beyond urging that conversation.
About a quarter to a third of weight lost on these medicines can be lean tissue if protein and training are neglected — a figure that matters more than the headline percentage, because muscle is what keeps you strong, keeps your metabolism higher, and keeps the loss looking and feeling like health rather than shrinkage. The defense is simple and boring: eat enough protein every day (the 1.6 to 2.2 grams per kilogram range used by our protein calculator is the evidence-based anchor for people losing weight), train against resistance two to four times a week, and do not chase the fastest possible loss. A slower loss with preserved muscle beats a faster loss that strips it, both for how you look and for how likely the weight is to stay off. Sleep belongs in the same paragraph: short sleep raises hunger hormones and reduces the proportion of fat in what you lose, so seven to nine hours is part of the program, not a luxury around it. For the full picture, pair this timeline with our TDEE calculator to see how your maintenance calories fall as you lose, and our calorie deficit calculator to plan a deficit that does not starve the muscle you are trying to keep.
The most useful thing to send a friend is not the headline percentage but the shape of the curve: slow first month, steep middle, flat tail — and the regain warning if treatment stops. Pin this page for the worked examples table, and send it to someone who is comparing the two medicines and wants the head-to-head number (20.2% versus 13.7% at 72 weeks) rather than two separate advertisements.
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<iframe src="https://livefitnesscheck.com/glp-1-weight-loss-timeline.php" width="100%" height="900" style="border:0"></iframe><p>Via <a href="https://livefitnesscheck.com/glp-1-weight-loss-timeline.php">GLP-1 Weight-Loss Timeline</a></p>Written by the Live Fitness Check editorial team · Reviewed against our calculator methodology · Last updated November 2026
Disclaimer: This tool is for educational purposes only and is not medical advice. It shows trial averages, not predictions for you, and it gives no dosage advice. GLP-1 medicines are prescription medicines with benefits and risks that only your clinician can weigh for your situation. Talk to your doctor before starting, stopping, or changing any medicine.