What a Calorie Deficit Is and Why It Matters on GLP-1 Medication
Your body burns a certain number of calories each day just to keep you going — this is your Total Daily Energy Expenditure (TDEE). When you eat less than that amount, the gap is your calorie deficit, and over time that deficit is what drives fat loss. On a GLP-1 medicine like tirzepatide (Mounjaro) or semaglutide (Wegovy), reduced appetite often creates a natural deficit — but many people find it useful to understand roughly how large that deficit is, rather than leaving it entirely to guesswork.
How the calculation works
The calculator uses your weight, height, age, sex, and activity level to estimate your TDEE, then subtracts a modest, general-purpose reduction to give you a starting deficit range. These figures are educational estimates, not a personal prescription — individual needs vary, and any specific calorie targets should be discussed with your prescriber or a registered dietitian who knows your full history.
What counts as a reasonable deficit?
General nutritional guidance (aligned with NHS principles) typically points toward a moderate deficit — often in the region of 500 calories per day as a common reference point — rather than very large cuts that can lead to fatigue, muscle loss, or nutrient gaps. On GLP-1 medication, where appetite is already suppressed, many people benefit from focusing on eating enough protein and nutrients within a reduced intake, rather than cutting as aggressively as possible. For more context on how to set these numbers, see our calorie deficit calculator guide and the related NHS-aligned deficit reference.
A note on the "free calorie deficit calculator" you may have seen elsewhere
Several national health services, including NHS-affiliated tools, publish free online calculators. These are useful references, and our calculator draws on the same widely accepted formulas (such as the Mifflin-St Jeor equation) that underpin most reputable tools. The numbers you get here are comparable in methodology, designed to be useful wherever you are in the world. For a broader look at how calorie calculations fit together, visit our calorie calculator hub.
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Tracking Your Calorie Deficit Automatically with GLP Trackr
Calculating a deficit is one thing — hitting it consistently day after day is where most people find the challenge. GLP Trackr's food logging feature is built around making that as effortless as possible, especially when appetite changes make it hard to judge portions or remember what you ate.
AI photo scan: point, snap, done
Rather than manually searching every ingredient, you can simply point your phone camera at a meal and let the AI food scanner estimate the calories, protein, and macros instantly. For people on GLP-1 medication who are eating smaller amounts and want quick logging without friction, this tends to be the feature that makes the biggest difference to consistency.
Set your deficit as a daily target
Once you know your number from the calculator above, you can enter it as a daily calorie target inside GLP Trackr. The app tracks your intake against that target throughout the day, so you always know where you stand — without mental arithmetic. You can also set a protein target alongside it, which matters especially on a GLP-1 journey where preserving muscle is important. For a deeper look at how deficit figures feed into the wider picture, the extended calorie deficit calculator covers additional variables worth exploring.
GLP Trackr is free to download and includes a 7-day trial — available on the App Store for iPhone and on Google Play for Android. If you have been looking for a free calorie deficit calculator app for iPhone or Android that understands GLP-1 life, this is built exactly for that. Give it a try: download GLP Trackr, enter your target from the calculator above, and let the app keep the numbers in check while you focus on the journey. Start your free 7-day trial on the App Store or Google Play today.
GLP Trackr is an information and tracking tool — it is not a substitute for advice from your prescriber or doctor. If you have questions about your calorie intake, weight management goals, or how your medication is working, always discuss them with your healthcare professional.
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Frequently asked questions.
A calorie deficit calculator estimates how many calories your body burns daily (your TDEE), then shows you a reduced intake target that creates a deficit. It uses your weight, height, age, sex, and activity level. The result is a general educational estimate, not a personalised medical prescription.
Yes — reputable free calculators, including this one, use established formulas consistent with mainstream nutritional guidance. NHS resources also reference similar principles. Results are estimates; for personalised advice, speak with your prescriber or a registered dietitian.
That decision belongs with your prescriber or a registered dietitian, as individual needs vary. General guidance often references a moderate deficit — avoiding very large cuts that can reduce protein intake, energy, and muscle mass. Your healthcare professional can advise what is appropriate for you.
GLP Trackr is available free on the App Store for iPhone (and Google Play for Android). It lets you set a daily calorie deficit target, log food via AI photo scan or barcode, and track your intake automatically — with a 7-day free trial included.
Yes — many people already on Mounjaro or Wegovy find it helpful to understand their energy balance. The calculator gives general estimates. Always follow your prescriber's guidance on diet and nutrition alongside your medication, as they know your full health picture.