How much weight might I lose? Weight-loss projection
Based on the STEP-1 trial (semaglutide 2.4mg, ~68 weeks) and the SURMOUNT-1 trial (tirzepatide 15mg, ~72 weeks), this calculator applies each drug's average percentage weight loss to your current weight. Trial averages vary widely between individuals — use this as a directional estimate, not a promise.
Weight-loss projection
How much protein do I need? Daily protein target
On a GLP-1, eating less makes it easy to under-eat protein — which accelerates muscle loss. The general guidance for people on weight-loss medication is 1.2–1.6g of protein per kilogram of bodyweight per day. Enter your weight below to get your daily range.
Protein target
Do I qualify? BMI & eligibility checker
GLP-1 medications are generally considered for adults with a BMI of 30 or above, or a BMI of 27 or above with at least one weight-related condition (such as type 2 diabetes, high blood pressure, or sleep apnoea). This tool calculates your BMI and gives you a plain-English note on where it sits relative to those general thresholds. Eligibility is always decided with a clinician.
BMI & eligibility checker
How much muscle could I lose? Muscle-loss estimator
Without resistance training and adequate protein, research suggests that roughly 20–40% of total weight lost during a calorie deficit can come from lean muscle rather than fat. With muscle-protective habits in place, that proportion drops substantially. This tool gives you an illustrative range for a planned weight loss — it is not a prediction, but it makes the stakes concrete.
Muscle-loss estimator
What's my BMR? Basal metabolic rate calculator
Your Basal Metabolic Rate (BMR) is the number of calories your body burns at complete rest just to keep you alive — breathing, circulation, cell repair. This calculator uses the Mifflin-St Jeor equation, widely regarded as the most accurate BMR formula for the general population.
BMR calculator
What's my TDEE? Total daily energy expenditure
Your Total Daily Energy Expenditure (TDEE) is your BMR plus the calories you burn through daily movement and exercise — it's roughly how many calories you'd need to eat to maintain your current weight. Enter your BMR (from the calculator above) and your activity level.
TDEE calculator
How big should my calorie deficit be?
Losing weight comes down to eating fewer calories than you burn. This calculator uses the standard rule that roughly 7,700 kcal (about 3,500 kcal per pound) of cumulative deficit corresponds to about 1kg of weight loss, to estimate the daily deficit needed for your target pace of loss.
Calorie deficit calculator
Frequently asked questions
Are these calculators medically accurate?
They apply published clinical-trial averages and widely used nutritional guidelines. Every individual is different — age, sex, starting weight, medication dose, adherence, diet, and activity level all influence real-world outcomes. Use the numbers as useful context, not a forecast.
Which trial data are used for the weight-loss projection?
The semaglutide figure (~15%) is based on the STEP-1 trial (Wilding et al., NEJM 2021). The tirzepatide figure (~20%) is based on the SURMOUNT-1 trial (Jastreboff et al., NEJM 2022). Both figures reflect the highest-dose arms of those trials over the full treatment period.
Should I use my current weight or goal weight for the protein calculator?
Most clinicians recommend using your current body weight (or a midpoint between current and goal) when calculating protein targets during active weight loss. The aim is to preserve lean mass, so the higher the target the better — especially on a GLP-1 where appetite suppression makes it easy to under-eat.
Does BMI alone determine GLP-1 eligibility?
No. BMI is one factor. Clinicians also consider comorbidities, cardiovascular risk, previous weight-loss attempts, medication history, and contraindications. A BMI of 27–30 may still qualify with certain weight-related conditions. Eligibility is always an individual clinical decision.
Can I prevent all muscle loss on a GLP-1?
Complete prevention is unrealistic during significant calorie restriction, but the muscle-loss proportion can be substantially reduced with resistance training 2–3 times a week and hitting a protein target of 1.2–1.6g per kilogram of bodyweight. See our guides on muscle loss on Ozempic and protein on a GLP-1 for the detail.
How is BMR calculated?
This tool uses the Mifflin-St Jeor equation — (10 × weight in kg) + (6.25 × height in cm) − (5 × age) + 5 for men, or − 161 for women. It's the formula most consistently validated against measured metabolic rate in research studies.
How is TDEE calculated?
TDEE is your BMR multiplied by an activity factor — 1.2 for sedentary up to 1.9 for extremely active. It's a widely used estimate, but real-world energy burn from exercise varies a lot between individuals, so treat the result as a starting point to adjust from.
How many calories should my daily deficit be?
A commonly used rule is that about 7,700 kcal of cumulative deficit corresponds to roughly 1kg of weight loss (about 3,500 kcal per pound). Dividing your target weekly loss by 7 gives an estimated daily deficit — pair it with an adequate protein target to help protect muscle.