GLP-1 Weight Loss Calculator
Where your weight goes, week by week, on semaglutide, tirzepatide, or one of the new oral GLP-1s. The curve is fitted to the published phase-3 trial means — not to a marketing number and not to somebody's before-and-after.
Projection
Weight at week 72
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Total lost
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% of body weight
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Time to goal
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BMI now → then
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Category now
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Category then
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Where these numbers come from
Each option is anchored to one published phase-3 trial, at that trial's own endpoint:
- Tirzepatide (Zepbound) — SURMOUNT-1, NEJM 2022. −15.0% / −19.5% / −20.9% at week 72 for 5 / 10 / 15 mg.
- Semaglutide 2.4 mg (Wegovy) — STEP 1, NEJM 2021. −14.9% at week 68.
- Oral semaglutide 25 mg (Wegovy pill) — OASIS 4, NEJM 2025. −13.6% at week 64.
- Orforglipron 36 mg (Foundayo) — ATTAIN-1, NEJM 2025. −11.2% at week 72.
- Liraglutide 3.0 mg (Saxenda) — SCALE, NEJM 2015. −8.0% at week 56.
Where a trial published two figures we use the lower one — the all-randomized number that counts people who quit, missed doses, or cut back for side effects. The higher "if you took every dose" figures were 17.3% for semaglutide and 22.5% for tirzepatide 15 mg. The conservative number is the honest default; the adherence field is there if you want to move it in either direction.
The formula
Every one of these trials draws the same shape: fast loss for about six months, a bend, then a plateau. A single exponential approach to an asymptote reproduces it with one parameter:
lost(t) = plateau × (1 − e−t/20), with t in weeks
The 20-week time constant reproduces the published interim means to within about one percentage point. plateau is then back-solved for each drug so the curve passes exactly through that trial's published endpoint — so the number at week 68 for semaglutide is 14.9%, by construction, not by luck.
Worked example
A 240 lb person on tirzepatide 15 mg. The trial mean is 20.9% at week 72, so the fitted asymptote is 20.9 ÷ (1 − e−72/20) = 21.5%. At week 72 the curve gives 240 × (1 − 0.209) = 189.8 lb — a 50 lb loss. Getting to a 190 lb goal (a 20.8% loss) takes about 68 weeks. Getting to 180 lb would require a 25% loss, which sits past the asymptote: this model says that goal isn't reachable on this dose alone, and it tells you so rather than quietly returning a giant number.
What this can't know
These are population means, and the spread around them is enormous. In SURMOUNT-1 roughly 40% of people on 15 mg lost more than 25% of their body weight while others lost almost nothing. Response depends on things no calculator has: your starting BMI, whether you have type 2 diabetes (weight loss on these drugs is consistently smaller with diabetes), how far you actually titrate, what you eat, and whether you keep lifting. Treat the curve as a centre line with a wide band around it, not a schedule.
FAQ
Why is my real weight loss slower than this in the first two months?
Because you're still titrating. Every one of these trials spends 4–5 months escalating the dose — semaglutide takes 16 weeks to reach 2.4 mg, tirzepatide 20 weeks to reach 15 mg. The fitted curve smooths over that ramp, so it runs slightly ahead of reality early and catches up by month six. If you're two months in and behind the line, that's expected.
What happens after the plateau?
In the two-year data (STEP 5), the plateau held: people who stayed on semaglutide were still down about 15% at week 104. The plateau is not a stall you push through — it's where the drug's effect and your new maintenance intake balance out. Losing further from there generally means a dose increase, a different drug, or a change in what you eat.
Does this work the same if I have type 2 diabetes?
No, and it's a large difference. The trials behind these numbers deliberately excluded people with type 2 diabetes. In the parallel diabetes trials (STEP 2, SURMOUNT-2) the same drugs at the same doses produced roughly two-thirds of the weight loss. If you have T2D, mentally scale these numbers down by about a third, or set adherence to ~65% to approximate it.
Should I pick the drug with the biggest number?
Not on its own. Tirzepatide 15 mg has the largest published mean, but it also has the highest cost, the most GI side effects at the top dose, and the most supply volatility. The oral options lose less on average and are far easier to live with. The right comparison is loss per dollar and per side effect you'll actually tolerate — which is what the GLP-1 cost calculator is for.
Is this medical advice?
No. It's arithmetic on published trial averages. It can't tell you whether a GLP-1 is appropriate for you, which one, or at what dose — those are prescriber decisions that depend on your history, your other medications, and your labs. Nothing here should change what you take.
Estimate — not medical advice
This is an estimate, not medical advice, and not a diagnosis. It doesn't know your history, your medications, or your other results, and it should never be used to start, stop, or change treatment. If a number here concerns you, take it to a doctor or pharmacist rather than acting on it.