Future you

This is a projection, not a prediction

The numbers this tool shows come from two large randomized trials. STEP 1 (Wilding et al., NEJM, 2021) followed 1,961 adults with obesity on 2.4mg weekly semaglutide for 68 weeks and found an average 14.9% body weight reduction against 2.4% on placebo. SURMOUNT-1 (Jastreboff et al., NEJM, 2022) followed 2,539 adults on 5mg, 10mg, or 15mg weekly tirzepatide for 72 weeks and found averages of 15.0%, 19.5%, and 20.9%.

Averages hide a lot. Some participants lost over 30% of body weight. Others lost under 5%. The tool shows you the middle half of the distribution (25th-75th percentile) because that\u2019s where most people actually land, not where a marketing page would put the arrow.

Don\u2019t treat the output as your future. Treat it as the shape of a reasonable expectation if everything goes roughly the way it went for trial participants. Your body, your adherence, and your clinician\u2019s titration plan do the real work.

How the projection is built

The tool uses a two-layer model. The first layer is a piecewise rate curve that maps week number to expected loss per week. The curve is flat and slow for the first 16 weeks (titration phase, where dose is still climbing), steepest from weeks 17 to 40 (therapeutic dose, primary loss phase), tapers from weeks 41 to 52 (approaching plateau), and flattens toward week 68 and beyond (maintenance).

The second layer anchors the curve to trial endpoints. For semaglutide, the endpoint is 14.9% at week 68 from STEP 1. For tirzepatide, it\u2019s 20.9% at week 72 from SURMOUNT-1 on 15mg, scaled down for 10mg (19.5%) and 5mg (15.0%). The curve integrates to match those endpoints, then interpolates backward to give you 3-month and 6-month milestones.

The 25th to 75th percentile band comes from the published trial distributions. STEP 1 reported that 69.1% of participants reached 10% loss, 50.5% reached 15%, and 32.0% reached 20%. SURMOUNT-1 reported 50% of 15mg participants reached 22.5%. The model fits a log-normal distribution to these published quantiles and extracts the 25th and 75th percentile curves alongside the mean.

A few caveats. The trial participants had BMI \u2265 30 or \u2265 27 with one comorbidity; the model doesn\u2019t check whether you match that. Trial participants got lifestyle counseling (500-kcal deficit target, 150 min/wk activity); the model assumes you do too. Real-world response may be lower on average than trial response because adherence is usually worse outside a trial setting.

Why your number will vary from the projection

Adherence. The biggest single factor. Trial participants took their injection on schedule. Real-world miss rates of 10-20% per year are common. Each missed week shifts the curve right.

Starting BMI. People with higher baseline BMI tend to lose more absolute pounds but similar percentages. STEP 1 subgroup analysis showed the 14.9% result held across BMI strata, but those below 30 lost slightly less.

Metabolic rate and body composition. Lower resting metabolic rate, lower muscle mass, menopausal status, and thyroid function all shift the curve. STEP 5 (Garvey et al., Nature Medicine, 2022) followed patients for 104 weeks and found women with postmenopausal status lost on average 1-2 percentage points less than premenopausal women at equivalent doses.

Titration speed. The label schedule takes 16-20 weeks to reach therapeutic dose. Going slower because of side effects can push 6-month milestones to month 8 or 9. Jumping ahead of the schedule rarely accelerates loss; it usually just increases nausea.

Concurrent medications. Steroids, some antipsychotics (olanzapine, clozapine), some antidepressants (paroxetine, mirtazapine), beta blockers, insulin, and sulfonylureas all tend to slow weight loss. Stimulants and thyroid replacement can speed it up.

STEP and SURMOUNT extensions. STEP 5 (104-week follow-up) and SURMOUNT-4 (withdrawal) tell us something important: people who stop lose the benefit, and people who continue tend to plateau around month 15-18 rather than keep losing forever.