GLP-1 muscle & weight-loss calculator

How this is calculated (and the research behind it)

Resting metabolism (BMR). The calculator uses the Mifflin-St Jeor equation, the predictive equation validated as most accurate for healthy adults.¹ For women it is 10 × weight(kg) + 6.25 × height(cm) − 5 × age − 161; for men the last term is + 5.

Total burn (TDEE). BMR is multiplied by a physical-activity factor (1.2 sedentary to 1.9 very active), the standard way to scale resting metabolism to real-world expenditure.² Your calorie target is TDEE minus the deficit implied by your chosen pace.

Weight-loss trajectory. The pace-to-deficit conversion uses the classic estimate that about 7,700 kcal equals one kilogram of body weight (3,500 kcal per pound).³ This is a first approximation. Real loss slows over time as metabolism adapts, so a dynamic model predicts less than a straight line at the far end.⁴ Treat the timeline as a planning estimate, not a promise.

Protein target. The 1.6 to 2.2 g/kg range comes from lean-mass research, where benefit to fat-free mass leveled off near 1.6 g/kg.⁵ It is split across four meals because distribution matters more than any single dose.⁶

The two muscle lines. Reviews of the trial data put lean mass at roughly 15 to 40 percent of the weight lost on a GLP-1.⁷ The red line models the higher end that occurs without countermeasures. The green line models the outcome with adequate protein and resistance training, using the finding that resistance training offset about 93.5 percent of the lean mass that caloric restriction alone would cost.⁸ These are illustrative projections from published ranges, not a measurement of your body.

Honest limits

Every number here is an estimate. Predictive BMR equations carry error at the individual level, the 7,700 kcal rule overstates loss over months, and the muscle split is modeled from population ranges rather than a scan of you. A target scaled to total body weight is a starting point, not a prescription, and it can overestimate protein for people carrying more fat mass. Use this as a framework, and confirm the specifics with your clinician, especially the calorie floor while on a GLP-1.