Almost every "GLP-1 before and after" article on the internet uses cherry-picked photos and lump-sum percentage claims that obscure what the medication actually does for an actual patient over an actual year. This article does the opposite. We pulled the day-by-day weight-loss curves from the published phase-3 trials of tirzepatide (SURMOUNT-1) and semaglutide (STEP-1), broke them down by starting weight category, and built a realistic timeline of what a patient should actually expect at 90 days, 180 days, and 365 days on each medication.
No fabricated testimonials. No transformation photos. Just published trial data from peer-reviewed sources, organized so a real patient can predict their realistic trajectory.
The trials we drew from
The published clinical evidence base for both major GLP-1 weight-loss medications is unusually strong, and the per-week weight-loss data is in the public record. Our two anchor trials:
SURMOUNT-1 (Jastreboff et al., NEJM 2022): 2,539 adults with obesity (without type 2 diabetes), randomized to placebo or tirzepatide at 5 mg, 10 mg, or 15 mg weekly. Primary endpoint at 72 weeks. Mean baseline body weight: 104.8 kg. The 15 mg arm achieved mean body weight reduction of approximately 20.9% at the 72-week endpoint.
STEP-1 (Wilding et al., NEJM 2021): 1,961 adults with overweight or obesity (without type 2 diabetes), randomized to placebo or semaglutide 2.4 mg weekly. Primary endpoint at 68 weeks. Mean baseline body weight: 105.3 kg. The semaglutide arm achieved mean body weight reduction of approximately 14.9% at the 68-week endpoint.
Both trials published intermediate weight-loss data points throughout the titration and maintenance phases, which is what allows us to model the day-by-day curve rather than just the end-state percentage.
Tirzepatide: the day-by-day curve at maintenance dose
For a patient titrating to the 15 mg/week tirzepatide maintenance dose (the SURMOUNT-1 highest dose arm), the typical weight-loss progression looks like:
| Time point | Mean % weight loss | For 100 kg (220 lb) patient | For 130 kg (286 lb) patient |
|---|---|---|---|
| Day 30 (titrating, 2.5 mg) | ~1.5% | 1.5 kg / 3.3 lb | 2.0 kg / 4.4 lb |
| Day 60 (titrating, 5 mg) | ~3.5% | 3.5 kg / 7.7 lb | 4.6 kg / 10.1 lb |
| Day 90 (titrating, 7.5 mg) | ~5.5% | 5.5 kg / 12.1 lb | 7.2 kg / 15.8 lb |
| Day 120 (10 mg) | ~8% | 8 kg / 17.6 lb | 10.4 kg / 22.9 lb |
| Day 180 (12.5-15 mg) | ~12% | 12 kg / 26.4 lb | 15.6 kg / 34.4 lb |
| Day 270 (15 mg) | ~17% | 17 kg / 37.4 lb | 22.1 kg / 48.6 lb |
| Day 365 (15 mg) | ~19% | 19 kg / 41.8 lb | 24.7 kg / 54.4 lb |
| Week 72 (SURMOUNT-1 endpoint) | ~20.9% | 20.9 kg / 46 lb | 27.2 kg / 60 lb |
The shape of the curve is the part that surprises most patients. Weight loss in the first 90 days is real but modest — typically 5-7% — because the patient is still titrating up through 2.5, 5, and 7.5 mg doses with relatively limited appetite suppression at the lower tiers. The steepest part of the curve happens between day 90 and day 270, once the patient reaches 10-15 mg. By month 12, most of the year-1 loss has occurred, and the curve flattens significantly heading into year 2.
Semaglutide: the day-by-day curve at 2.4 mg/week
| Time point | Mean % weight loss | For 100 kg patient | For 130 kg patient |
|---|---|---|---|
| Day 30 (0.25 mg) | ~1% | 1 kg / 2.2 lb | 1.3 kg / 2.9 lb |
| Day 60 (0.5 mg) | ~2.5% | 2.5 kg / 5.5 lb | 3.3 kg / 7.2 lb |
| Day 90 (1.0 mg) | ~4% | 4 kg / 8.8 lb | 5.2 kg / 11.4 lb |
| Day 120 (1.7 mg) | ~6% | 6 kg / 13.2 lb | 7.8 kg / 17.2 lb |
| Day 180 (2.4 mg) | ~9% | 9 kg / 19.8 lb | 11.7 kg / 25.7 lb |
| Day 270 (2.4 mg) | ~12% | 12 kg / 26.4 lb | 15.6 kg / 34.4 lb |
| Day 365 (2.4 mg) | ~14% | 14 kg / 30.8 lb | 18.2 kg / 40.1 lb |
| Week 68 (STEP-1 endpoint) | ~14.9% | 14.9 kg / 32.8 lb | 19.4 kg / 42.7 lb |
Semaglutide's curve has the same general shape as tirzepatide's but the magnitude is meaningfully smaller. At every comparable time point, semaglutide produces roughly 60-75% of the weight loss of tirzepatide at maximum dose. This is the consistent finding across head-to-head comparisons (most directly the SURMOUNT-5 trial, which compared the two drugs head-to-head and found tirzepatide superior).
Both drugs are GLP-1 agonists, but tirzepatide is also a GIP receptor agonist — it activates a second gut hormone pathway in addition to GLP-1. The dual mechanism appears to produce a meaningfully greater appetite-suppression effect, which translates to greater weight loss across the dosing range. This is the reason most newer telehealth providers default to tirzepatide rather than semaglutide when both are available.
By starting weight: what you can realistically expect
The percentages above are means. The absolute amount of weight a patient loses depends heavily on their starting body weight. Here is the realistic 365-day weight-loss expectation by starting BMI category, on tirzepatide 15 mg/week:
| Starting weight | BMI category | Likely loss at 365 days | Likely loss at 72 weeks |
|---|---|---|---|
| 180 lb (82 kg) | Overweight (BMI 27-29.9) | ~34 lb | ~38 lb |
| 220 lb (100 kg) | Obesity class I (BMI 30-34.9) | ~42 lb | ~46 lb |
| 250 lb (113 kg) | Obesity class II (BMI 35-39.9) | ~48 lb | ~52 lb |
| 300 lb (136 kg) | Obesity class III (BMI 40+) | ~57 lb | ~63 lb |
| 350 lb (159 kg) | Severe class III | ~66 lb | ~73 lb |
These numbers are mean trajectories; individual results vary substantially. About one-third of patients in SURMOUNT-1 lost more than 25% of body weight at 72 weeks; about one-third lost between 15% and 25%; about one-third lost less than 15%. A small minority (under 10%) lost less than 5% and were considered non-responders.
Why your individual curve will differ
The published trial means are useful baselines, but real-world patients deviate from them for at least six predictable reasons:
1. Maximum tolerated dose. Not every patient reaches 15 mg of tirzepatide. Side effects (nausea, fatigue, GI symptoms) limit some patients to 5 or 10 mg as their long-term dose. Lower max dose = lower expected weight loss.
2. Adherence. Trial participants under study supervision have higher adherence than typical real-world patients. Missed doses, gaps in supply, or skipped weeks reduce cumulative effect.
3. Concurrent lifestyle changes. Patients who pair the medication with even modest dietary attention and added physical activity consistently outperform the trial means. Patients who treat the medication as the entire intervention typically underperform.
4. Starting metabolic profile. Patients with insulin resistance, prediabetes, or metabolic syndrome often respond more strongly to the appetite-suppression effect than patients without these factors.
5. Sex and age effects. Women in SURMOUNT-1 lost slightly more weight on average than men. Older patients lost slightly less than younger patients. Both effects are modest but real.
6. Genetic variability. A subset of patients are clear "super-responders" who lose 30%+ of body weight; another subset are clear non-responders who lose less than 5%. The biological basis is partially understood but not currently testable in a clinical setting. The only way to find out which group you are in is to titrate and observe.
The clinical practice guideline for both tirzepatide and semaglutide recommends evaluating response at 12-16 weeks at the maintenance dose. A patient who has not lost at least 5% of body weight by that point is unlikely to achieve a clinically meaningful response and should discuss alternatives with their prescriber. Most providers will continue the medication as long as the patient is losing at any rate; some plans require the 5% threshold for continued coverage.
What happens after 365 days
The curve flattens significantly after the first year, but does not stop. SURMOUNT-1 showed continued (slower) weight loss between months 12 and 18 in the 15 mg arm, with most patients reaching their nadir somewhere between month 15 and month 24. STEP-5 (a longer follow-up of semaglutide) showed similar continued loss into year 2.
The bigger question for patients reaching maintenance is what happens when the medication stops. The published evidence is sobering: the STEP-4 trial randomized patients who had achieved weight loss on semaglutide to either continue or switch to placebo. The continuation arm continued losing weight; the placebo arm regained roughly two-thirds of their lost weight within 12 months. The implication for most patients is that GLP-1s are appropriately conceptualized as a long-term medication for a chronic condition rather than a short-term cycle.
For most patients in 2026, the question is not "how much will I lose in year 1" — the trial data is consistent and predictable. The harder question is "what does year 3, year 5, year 10 look like?" That evidence base is still maturing.
The takeaway
You can predict your first year on tirzepatide or semaglutide with reasonable accuracy from the published trial data. The mean trajectory is roughly 5% loss at 90 days, 12% at 180 days, and 19-21% at 365 days for tirzepatide 15 mg; 4%, 9%, and 14-15% respectively for semaglutide 2.4 mg. Your individual results will vary above or below these means based on your maximum tolerated dose, adherence, lifestyle context, and individual biology.
The "before and after" photos that dominate online weight-loss content are heavily selected and rarely representative. The trial data is. Build your expectations from the data, not from the marketing.
For provider-by-provider pricing of tirzepatide and semaglutide programs, see The Cheapest GLP-1 in 2026. For the brand-vs-compounded breakdown of the same molecules, see Mounjaro vs Zepbound 2026.