The Numbers You Need: BMR, Maintenance Calories, and Your Deficit
Three figures build the picture: your Basal Metabolic Rate (BMR), your Total Daily Energy Expenditure (TDEE or maintenance calories), and your target deficit.
Step 1 — Work out your BMR
Your BMR is the number of calories your body burns at complete rest, just to keep basic functions running. It is calculated from your weight, height, age, and sex. The most widely used formula is the Mifflin-St Jeor equation. As a rough guide, many adults have a BMR somewhere between 1,400 and 2,000 kcal, though individual variation is significant — treat any formula result as an estimate, not a precise prescription.
Step 2 — Work out your maintenance calories
Multiply your BMR by an activity factor (commonly 1.2 for mostly sedentary, up to 1.725 for very active) to get your TDEE — the calories needed to stay at your current weight. For a practical walkthrough of this calculation, see our guide on how to calculate your maintenance calories.
Step 3 — Set a deficit
A calorie deficit means eating fewer calories than your TDEE. A commonly referenced moderate deficit is around 500 kcal per day, which general nutrition guidance associates with roughly 0.5 kg of weight loss per week. Steeper deficits are not always better — on a GLP-1 medicine, appetite suppression can already push intake low, making adequate protein and micronutrient intake harder. General guidance suggests most adults should not go below around 1,200–1,500 kcal without clinical supervision, but the right level for you is a conversation for your prescriber or doctor.
Understanding how to count the calories in what you eat is the practical companion to knowing your deficit target — the two figures only mean something together. For a deeper look at the full deficit calculation process, our page on how to calculate a calorie deficit walks through each step in detail. All of this sits within our broader calorie deficit guide for GLP-1 users.
average weekly weight change in the first 16 weeks of Mounjaro & Wegovy use*
Tracking the right four numbers — weight, waist, protein and dose — turns a noisy chart into a clear story. That's the loop GLP-1 users keep coming back for.
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How GLP Trackr Handles the Maths for You
Calculating a deficit manually is useful once; doing it every day is where most people fall off track. GLP Trackr's food logging removes the friction: point your camera at a meal and the AI photo scan returns an instant calorie and macro breakdown — no searching, no guesswork, no manual entry required.
Once your calorie and protein targets are set inside the app, every meal you log is measured against them automatically. You can see at a glance whether you are hitting your deficit or under-eating — both matter on a GLP-1 journey where appetite signals can be unreliable. The daily check-in also captures weight each morning, so your deficit targets and your actual results are tracked in the same place, and the app's insights surface patterns across the two over time.
GLP Trackr is a tracking tool, not a clinical service. The numbers it helps you log are most useful when you bring them to your prescriber or doctor — they can advise on whether your deficit is appropriate for your health history, something no app can do for you.
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Frequently asked questions.
Subtract your daily calorie intake from your Total Daily Energy Expenditure (TDEE). First calculate your BMR using your weight, height, age, and sex, then multiply by an activity factor to get your TDEE. The difference between TDEE and what you eat is your deficit.
Your BMR is estimated using a formula — the Mifflin-St Jeor equation is widely used — based on your weight, height, age, and sex. Online calculators apply this automatically. Treat the result as a useful estimate rather than a precise figure, as individual metabolism varies.
Multiply your BMR by an activity factor (typically 1.2 for sedentary to 1.725 for very active) to estimate the calories needed to maintain your current weight. On a GLP-1 medicine, reduced appetite may already place you below this level without you realising.
Once you know your calorie target, macros are split from that total. Many people on GLP-1 medicines prioritise protein — a common general target is 1.2–1.6 g per kg of body weight — with fat and carbohydrates making up the remainder. Your prescriber or doctor can advise on targets suited to your needs.
GLP Trackr lets you set a calorie target and logs every meal against it using AI photo scan, barcode, or manual search, so you can see your deficit in real time. It is a tracking tool; the right calorie target for you should be confirmed with your prescriber or doctor.