Calorie Deficit Calculator: Understanding Your Energy Gap on a GLP-1 Journey

Your calorie deficit is the gap between the energy your body uses each day — your total daily energy expenditure (TDEE) — and the calories you actually eat. Create a deficit consistently and your body draws on stored energy; eliminate it and progress tends to stall. Neither extreme is ideal: too large a deficit on a GLP-1 medicine can make it harder to hit protein targets and maintain muscle, while too small a gap may slow progress.

The basic calorie deficit formula

The calculation itself is straightforward:

• Calorie deficit = TDEE minus daily calorie intake
• A moderate deficit is commonly cited in nutritional guidance as roughly 300–500 kcal per day, though what works for any individual varies with body composition, activity, and health history
• Because GLP-1 medicines affect appetite and portion sizes, your actual intake may already be lower than you realise — which is exactly why tracking it matters

What goes into your TDEE?

TDEE combines your basal metabolic rate (the energy your body needs at rest) with the calories burned through daily movement and exercise. Factors that shift it include height, weight, age, biological sex, and activity level. Our maintenance calorie calculator walks through the numbers in more detail, and our weight-reduction calculator can help you explore what a target deficit might look like week to week.

General guidance from sources such as the NHS suggests that crash diets or very low calorie intakes are not suitable for everyone — particularly people on medication. Always discuss any significant change to your eating approach with your prescriber or doctor before acting on it.

Why this matters specifically on a GLP-1 medicine

Reduced appetite is one of the most commonly reported effects of tirzepatide and semaglutide. This is useful, but it also means some people under-eat without realising — consuming so few calories that protein intake suffers and fatigue sets in. Knowing your deficit gives you something concrete to work with rather than relying on hunger signals that may be quieter than usual. For a broader look at energy and nutrition tracking, visit our calorie tracking hub.

Calculating a deficit is one thing; knowing whether you are actually hitting it day to day is another. GLP Trackr's food logging feature takes the manual effort out of the equation — point your camera at a meal and the AI photo scan estimates calories, protein, and macros in seconds. For packaged food, the barcode scanner fills in the details instantly.

Once you have set a daily calorie target in the app, your running deficit is visible throughout the day without any arithmetic on your part. You can also set a protein target alongside it — important on a GLP-1 journey where appetite suppression can make it easy to under-eat protein even when overall calories look fine.

Over time, the insights section shows how your intake patterns relate to your weight trend, giving you a clearer picture of what is (and is not) moving the needle. That kind of data is also useful to bring to a prescriber appointment — far more concrete than a rough recollection of what you ate last week.

A note on targets: the numbers this calculator and the app produce are general educational starting points. Any decision about your calorie intake — especially if you have a medical condition or are on other medication — should be made in conversation with your prescriber or doctor, not on your own. GLP Trackr helps you record and understand your data; it is not a substitute for professional guidance.

Ready to stop guessing and start seeing your deficit clearly? Download GLP Trackr on the App Store or Google Play — your first 7 days are completely free.