Why does the curve flatten?

Appetite suppression meets a new energy equilibrium: as weight falls, calorie needs fall with it, and loss tapers toward a plateau. Trials show the same shape — steep first 6 months, ~95% of total loss by month 15. The plateau is expected physiology, not failure.

Which drug gives the most loss?

Tirzepatide. In the only large head-to-head trial (SURMOUNT-5, 72 weeks), tirzepatide averaged −20.2% versus −13.7% for semaglutide 2.4 mg. It usually costs more — the cost calculator shows whether the gap is worth it for your pathway.

What happens if I stop?

In the STEP 1 extension, participants regained about two-thirds of lost weight within a year of stopping semaglutide. Toggle “stop at month 12” above to see that curve. Plan maintenance — dose taper, lifestyle scaffolding or continued therapy — with your prescriber before stopping.

Do diet and exercise still matter?

Yes — every trial ran on top of a reduced-calorie diet and increased activity. Resistance training and protein intake also protect lean mass, which matters because up to a quarter of GLP-1 weight loss can be muscle. The lifestyle multiplier here is a modest proxy for that support.

Is compounded semaglutide as effective?

No head-to-head trials exist. Compounded projections here assume the same molecule titrated to an equivalent dose from a pharmacy operating within FDA rules — the pharmacokinetics should track the brand, but quality varies by pharmacy. Check the safety register before buying.

Weight loss projection (2026): what the trials say you’ll lose

Q: How accurate is this projection?

It reproduces trial-average trajectories well — ~70% of loss by month 6, plateau by 15 — but individuals scatter widely around every average. In STEP 1 about a third beat −20% while 1 in 7 lost under 5%. Treat the band, not the line, as the honest answer.

A month-by-month curve anchored to the STEP 1 and SURMOUNT trials, with the published figure for what happens to your weight after you stop.

How much will I lose, and by when? · Data: STEP 1 · SURMOUNT-1 · SURMOUNT-5 · Checked August 27, 2026

Your inputs

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Current weight (lb)

Goal weight (lb)

Medication

Diet & exercise effort

Scenario

Anchor: STEP 1, 68 wk — mean −14.9%.

Wegovy · 220 → 180 lb

Line: trial-average · band: middle range of responders · 24 months

Month 3

205 lb

−15 lb · −7.0%

Month 6

197 lb

−23 lb · −10.7%

Month 12

190 lb

−30 lb · −13.7%

Month 18

188 lb

−32 lb · −14.6%

Your goal (−18.2%) sits beyond the trial-average curve for Wegovy within 24 months — trials suggest tirzepatide-class medication gets materially closer (−20.9% mean at 72 wk).

Response varies widely: in STEP 1, roughly a third of participants lost over 20% — and about 1 in 7 lost under 5%. Trials pair medication with diet and activity support; the multiplier here is a rough proxy for that.

Cite this result: “At trial-average response, a 220 lb adult on Wegovy projects to about 190 lb at month 12 (−13.7%), anchored to STEP 1, 68 wk” — glp1.health weight loss projection, glp1.health/tools/weight-loss-projection, data as of August 27, 2026.

The trial anchors behind the model

Drug & dose	Mean loss	Trial
Wegovy (semaglutide 2.4 mg)	−14.9%	STEP 1, 68 wk · NCT03548935
Zepbound / Mounjaro (tirzepatide 15 mg)	−20.9%	SURMOUNT-1, 72 wk · NCT04184622
Ozempic ≤2 mg (diabetes dosing)	−7.0%	STEP 2 / SUSTAIN (T2D populations) · NCT03552757
Compounded semaglutide	−14.9%	Anchored to STEP 1 · NCT03548935
Compounded tirzepatide	−20.9%	Anchored to SURMOUNT-1 · NCT04184622
Head-to-head (tirzepatide vs semaglutide)	−20.2% vs −13.7%	SURMOUNT-5, 72 wk head-to-head

Source: peer-reviewed primary publications (NEJM), verified August 27, 2026. Ozempic diabetes dosing (≤2 mg) is anchored to T2D populations and loses materially less than Wegovy 2.4 mg.

Model output: expected % of body weight lost, by month

Month	Semaglutide 2.4 mg	Tirzepatide 15 mg
1	−2.8%	−4.0%
3	−7.0%	−9.8%
6	−10.7%	−15.0%
9	−12.6%	−17.7%
12	−13.7%	−19.2%
18	−14.6%	−20.4%
24	−14.8%	−20.8%

Model values at moderate lifestyle effort (multiplier 1.0), plateau constant k = 0.21 — calibrated so ~70% of total loss lands by month 6 and ~95% by month 15, matching published trial trajectories.

How this projection works

The curve is a plateau model: percent lost at month t = L × M × (1 − e^−0.21t). L is the mean total loss from each drug’s Phase 3 trial — STEP 1 for semaglutide 2.4 mg, SURMOUNT-1 for tirzepatide — and M is a lifestyle multiplier (0.85 / 1.0 / 1.15) standing in for the diet-and-activity support all trials included.

The shaded band spans roughly the middle range of trial responders (0.55–1.25× the expected curve) — distributions are wide, and some participants lose under 5%. The stop scenario applies the STEP 1 extension finding: about two-thirds of lost weight regained over the year after discontinuation.

Limits: trial populations (mostly BMI ≥30, without diabetes except where noted) may not match you; real-world adherence is lower than trial adherence; compounded formulations assume dose-equivalent titration. This is an educational estimate — treatment decisions belong with your prescriber.

Which drug for your goal? What trials suggest

Need >17% loss → tirzepatide-class

Only tirzepatide 15 mg averaged above 20% (SURMOUNT-1); semaglutide’s trial mean falls short of 17%.

Need 10–17% → semaglutide 2.4 mg or tirzepatide

Both trial means cover this range; price and tolerability usually decide (see the cost calculator).

Need <10% → a broader set qualifies

Lower doses and oral options reach single-digit means; the cheapest pathway may be enough.

Stopping is the plan’s weak point

Two-thirds of lost weight returned within a year in the STEP 1 extension — budget for maintenance before you start.

Questions

Projection questions, answered directly

It reproduces trial-average trajectories well — ~70% of loss by month 6, plateau by 15 — but individuals scatter widely around every average. In STEP 1 about a third beat −20% while 1 in 7 lost under 5%. Treat the band, not the line, as the honest answer.

Educational estimate, not medical advice and not a guarantee of individual results. Trials suggest ranges; your prescriber individualizes treatment. Talk to a licensed clinician before starting, stopping or changing a medication.

Data sources · cited with retrieval dates

FDA prescribing informationThe labels for every product a tool names, on the label holder’s own site
Manufacturer cash programsNovoCare, LillyDirect and TrumpRx published self-pay prices
CMS NADACNational Average Drug Acquisition Cost, weekly file

NADAC figures are pharmacy acquisition costs, not retail prices and not what you will pay. This content is educational and is not medical advice.

The data behind this tool · 7 pages

GLP-1 medications Dulaglutide online Exenatide online Liraglutide online Orforglipron online Semaglutide online Tirzepatide online