Sources & References
The calculator's weight-loss projections are derived from FDA phase 3 trial primary endpoints, and pricing data is sourced from public manufacturer and telehealth pages.
Clinical trials
- STEP-1 (Wegovy / semaglutide 2.4mg)14.9% mean weight loss at 68 weeks vs 2.4% placeboView source →
- SURMOUNT-1 (Zepbound / tirzepatide 15mg)22.5% mean weight loss at 72 weeksView source →
- OASIS-4 (oral semaglutide 25mg)13.6% mean weight loss at 68 weeksView source →
- SURPASS-2 (Mounjaro / tirzepatide for T2D)20.9% peak weight loss as off-label useView source →
- ATTAIN-1 (Foundayo / orforglipron)14.7% mean weight loss at 72 weeks (oral, non-peptide)View source →
- REDEFINE-1 (CagriSema / cagrilintide+semaglutide)20.4% mean weight loss at 68 weeksView source →
- SCALE (Saxenda / liraglutide)8.4% mean weight loss at 56 weeksView source →
Pricing references
- LillyDirect - manufacturer self-pay for Zepbound and orforglipron
- Foundayo Coverage & Savings (Eli Lilly) - official savings-card terms and dose-tier pricing for orforglipron (verified 2026-05-23)
- NovoCare - patient assistance for Wegovy, Ozempic, Saxenda
- GoodRx GLP-1 service
- Hims, Ro, Found, Lemonaid, LifeMD public pricing pages (May 2026 snapshot)
Modeling notes
We model weight loss as an exponential approach to plateau: pct(t) = peak × (1 - exp(-t / τ)) where τ = peakWeeks / 2.5. This produces curves that closely match published trial graphs at weeks 4, 12, 28, 52, and 68/72. The model assumes full adherence and does not account for plateaus, dose escalation, or weight regain after stopping.
Sex adjustment methodology
The calculator's sex toggle (Female / Male / Skip) applies a ±1.5 percentage-pointabsolute adjustment to each drug's peak weight-loss percentage. The 3-percentage-point total spread is the midpoint of the published female-vs-male differential reported in phase 3 subgroup analyses, applied symmetrically around the trial population mean. "Skip" uses the population mean (the unadjusted peak % from each trial).
Primary sources for the sex × weight-loss interaction:
- STEP-1 (Wegovy / semaglutide 2.4 mg) - Wilding JPH et al. N Engl J Med 2021;384:989-1002. Sex-stratified outcomes in supplementary appendix; female subgroup mean weight loss exceeded male subgroup at 68 weeks. View source →
- SURMOUNT-1 (Zepbound / tirzepatide) - Jastreboff AM et al. N Engl J Med 2022;387:205-216. Sex subgroup analyses for 5/10/15 mg dose tiers; same directional finding consistent across all arms. View source →
- STEP-2 (semaglutide 2.4 mg in type 2 diabetes) - Davies M et al. Lancet 2021;397:971-984. Sex subgroup consistent with STEP-1 in the diabetic population. View source →
Plausible mechanisms reported in the cardiometabolic literature: higher per-kg drug exposure in lower-body-weight patients, greater proportion of body fat responsive to GLP-1 satiety signaling, estrogen modulation of GLP-1 receptors, and higher real-world adherence in female patients.
Why age is not modeled
Age is a real factor in GLP-1 outcomes - older patients on the same drug + dose tend to lose somewhat less weight than younger patients due to lower basal metabolic rate, slower drug clearance, and sarcopenia. However, phase 3 trials report age subgroups with noisier effect sizes and overlapping confidence intervals, and we do not have a primary-source- citable magnitude that meets our editorial standard (every published number on this site must trace back to a peer-reviewed source - see Editorial Standards).
Rather than publish a number we can't directly cite, we leave age out of the weight-loss projection. If you are 65 or older, expect your individual outcome may run somewhat below the calculator's projection - and discuss titration pace with your prescriber, since slower drug clearance can amplify side effects at standard doses.
Pricing snapshot: May 2026. We update periodically.