Understanding Calorie Needs and Deficits for Weight Loss
Your total daily energy expenditure (TDEE) is the number of calories your body burns across everything — basic functions at rest, digestion, movement, and exercise. To lose weight, you generally need to consume fewer calories than this total. A commonly referenced general guideline is a deficit of around 500 calories per day to produce approximately 0.5 kg (1 lb) of loss per week, though this is an educational estimate rather than a personal prescription — actual results vary widely.
What affects your calorie target?
- Basal metabolic rate (BMR): the calories your body needs just to keep going at rest, influenced by height, weight, age, and biological sex.
- Activity level: the more active you are, the higher your maintenance calories and the more room you have to create a deficit without eating too little.
- Body composition: more muscle mass generally means a higher resting burn.
- GLP-1 medication effects: many people on tirzepatide or semaglutide find their appetite and portion sizes reduce significantly, so their actual intake may already be lower than expected — tracking helps you see exactly where you stand.
How low is too low?
Dropping calories too aggressively can lead to fatigue, muscle loss, and nutritional gaps. General guidance from nutrition organisations typically suggests most adults should not go below around 1,200–1,500 calories per day without medical supervision, but these figures are general and your own situation may differ. Always discuss specific targets with your prescriber or a registered dietitian who knows your full health picture.
For a broader look at what daily intake figures are commonly referenced, see our guides on daily calorie needs explained and how much a person typically needs in a day. You can also explore our calorie calculator hub for a full set of tools to work out your numbers.
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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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Track Your Calories Automatically with GLP Trackr
Knowing your target is one thing — actually tracking what you eat each day is where most people run into friction, especially when appetite changes mean meals are smaller, more irregular, or harder to plan. GLP Trackr makes food logging as effortless as pointing your camera: the AI photo scan identifies meals and estimates calories and macros instantly, so you do not need to weigh every ingredient or search a database manually.
Once your calorie and protein targets are set inside the app, your daily check-in and food log show you exactly where you are against those numbers in real time. Over time, the insights feature surfaces patterns — such as how your intake on different days relates to your energy levels or progress — giving you genuinely useful information to discuss with your prescriber or healthcare professional.
If you want a starting point for your calorie goal before using the tracker, our page on finding the right daily calorie amount walks through the key factors in plain language.
GLP Trackr is a tracking and journaling tool — it supports your journey and helps you understand your own data, but it is not a substitute for personalised advice from your prescriber or a dietitian. Any decision about your specific calorie target is best made with a healthcare professional who knows your full history.
Ready to put a number to your days? Download GLP Trackr on the App Store or Google Play and start your free 7-day trial — log meals by photo, set your calorie goal, and see your progress come together in one place.
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Frequently asked questions.
Most people create a calorie deficit of roughly 300–600 calories below their daily maintenance needs to lose weight. The exact figure depends on your size, age, and activity level. A personalised target is best discussed with your prescriber or a registered dietitian.
Many people on tirzepatide (Mounjaro) or semaglutide (Wegovy) find their appetite reduces and portion sizes naturally shrink, which can lower calorie intake. Tracking your actual food intake helps you understand where you stand and ensures you are still meeting nutritional needs.
General nutrition guidance suggests most adults should not consistently eat below around 1,200–1,500 calories without medical supervision, as very low intakes can cause fatigue and nutritional gaps. Your own minimum depends on your individual circumstances — always discuss this with your prescriber.
GLP Trackr's AI photo scan lets you log a meal just by taking a picture, making it easier to track even small or irregular portions. Setting a daily calorie target in the app shows you your intake in real time without the need for detailed manual logging.
A calorie deficit means consuming fewer calories than your body burns in a day. Over time, the body draws on stored energy — including fat — to make up the difference, which leads to weight loss. The size of the deficit, sustained consistently, is the main driver of the rate of loss.