How to Calculate GLP-1 Weight Loss Projection

What is GLP-1 Weight Loss Projection?

The GLP-1 Weight Loss Projection calculator estimates expected percentage of body weight loss over time based on clinical trial data for semaglutide and tirzepatide. It uses average weight loss curves from landmark trials like STEP and SURMOUNT to provide realistic month-by-month projections.

Formula

Projected Weight at Week W = Starting Weight × (1 - Expected %BWL at Week W / 100)

W₀: Starting Weight (lbs or kg) — Body weight at treatment initiation
%BWL: Expected Body Weight Loss (%) — Mean percentage weight loss from clinical trial data for selected medication and dose
W: Week Number (weeks) — Number of weeks since starting treatment
W_t: Target Weight (lbs or kg) — Projected weight at the given time point

Step-by-Step Guide

1Enter your current weight, height, and selected GLP-1 medication
2Choose your target dose and whether you are combining with lifestyle intervention
3The calculator plots a month-by-month weight loss curve based on clinical trial averages
4View projected weight at 3, 6, 12, and 18 months alongside clinical trial benchmarks

Worked Examples

Input

220 lbs starting weight on semaglutide 2.4 mg (Wegovy)

Result

Projected weight at 68 weeks: 220 × (1 - 0.149) = 187.2 lbs, a loss of 32.8 lbs (14.9% body weight per STEP 1 trial)

Input

250 lbs starting weight on tirzepatide 15 mg (Zepbound)

Result

Projected weight at 72 weeks: 250 × (1 - 0.208) = 198 lbs, a loss of 52 lbs (20.8% body weight per SURMOUNT-1 trial)

Common Mistakes to Avoid

✕Expecting linear weight loss — GLP-1 weight loss follows a curve that plateaus around 60-72 weeks
✕Not accounting for starting BMI: patients with higher BMI often lose a greater absolute amount but similar percentage
✕Comparing results directly between medications without considering dose differences and trial populations

Frequently Asked Questions

How much weight will I actually lose on Ozempic or Wegovy?

Clinical trials show average weight loss of 14.9% of body weight on semaglutide 2.4 mg (Wegovy) over 68 weeks. Individual results vary widely — some patients lose 20%+ while others lose less than 5%. Lifestyle modifications significantly improve outcomes.

Is tirzepatide more effective than semaglutide for weight loss?

Head-to-head data from the SURMOUNT trials show tirzepatide 15 mg achieves roughly 20.8% body weight loss vs. semaglutide's 14.9%, though direct comparison trials are ongoing. Both are significantly more effective than prior anti-obesity medications.

Ready to calculate? Try the free GLP-1 Weight Loss Projection Calculator

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