How to Work Out Your Calorie Deficit on a GLP-1 Journey

Working out your calorie deficit involves two numbers: your Total Daily Energy Expenditure (TDEE) — essentially your maintenance calories — and your target intake, which sits below it. The difference between the two is your deficit.

Step 1: Estimate your maintenance calories

Your TDEE is shaped by your Basal Metabolic Rate (BMR) — the calories your body burns at complete rest — plus an activity multiplier. A widely used formula (the Mifflin-St Jeor equation) estimates BMR from your weight, height, age, and sex, then multiplies by an activity factor ranging from sedentary to very active. If you want a structured walkthrough of this step, the guide on working out your maintenance calories covers it in detail.

Step 2: Choose a deficit size

A commonly referenced moderate deficit is around 500 calories per day below maintenance, which many nutrition educators associate with gradual, sustainable progress. Larger deficits are not necessarily better — eating too little can undermine muscle retention, energy, and the protein intake that matters particularly on a GLP-1 medicine. General educational guidance typically suggests staying above around 1,200–1,500 kcal depending on body size, but your own appropriate range is something to discuss with your prescriber or a registered dietitian, not something to set in isolation.

Step 3: Account for GLP-1 appetite changes

Because Mounjaro and Wegovy commonly reduce appetite and food noise, your actual intake may already sit well below your old maintenance level without deliberate effort. Tracking what you actually eat — rather than guessing — is the only reliable way to know whether your real deficit is too large, too small, or about right. For a deeper look at the maths involved, see the pages on working out your calorie deficit and how to calculate a calorie deficit for further context.

How to work out your macros alongside your deficit

Once you have a calorie target, splitting it into macronutrients — protein, carbohydrates, and fat — gives you a more complete picture. On a GLP-1 journey, protein is the macro most worth prioritising: it supports muscle retention during weight loss and tends to be more satiating per calorie. A general starting point referenced in nutrition literature is around 1.2–1.6 g of protein per kilogram of body weight per day, though individual needs vary. Carbohydrate and fat distribution can be adjusted around that protein anchor based on your preferences and how your digestion responds to the medicine. For the broader picture on calorie deficit planning, the calorie deficit hub brings all of these concepts together.

Calculating a deficit on paper is one thing; knowing whether you are actually hitting it day to day is another. GLP Trackr's AI food logging is the fastest way to close that gap — point your phone camera at a meal and the app estimates calories, protein, and macros instantly, without manual entry. On days when appetite is low and meals are small or irregular, that speed makes the difference between logging consistently and not logging at all.

Alongside photo scanning, you can set a personalised calorie and protein target inside the app, and the daily check-in keeps a running tally so you can see at a glance whether you are on track before the day is over. The insights dashboard then surfaces patterns over time — for example, whether the weeks where you hit your protein goal tend to correlate with stronger progress on the scale — giving you data to work with rather than guesswork.

GLP Trackr is free to try for 7 days and available on the App Store and Google Play. If calorie and macro tracking has felt like a chore in the past, the photo-scan feature alone tends to change that — give it a week and see how much easier it becomes to stay consistent.

A note on numbers: the figures above are general educational ranges, not a personal prescription. Your ideal calorie deficit and macro split depend on your individual health profile, activity level, and the guidance of your prescriber or a registered dietitian. Always discuss significant dietary changes with your healthcare professional, particularly if you are managing any other health conditions alongside your GLP-1 treatment.