How Many Calories Do You Need to Lose Weight?

A calorie is a unit of energy. Your body uses a baseline number of calories just to keep functioning — breathing, circulation, temperature regulation — and burns more through movement and activity. When you consistently consume fewer calories than you use, your body draws on stored energy, which over time results in weight loss.

The deficit principle in numbers

As a general educational reference point, 1 lb (roughly 0.45 kg) of body fat represents approximately 3,500 calories of stored energy. On that basis:

• A daily deficit of around 500 calories is often associated with losing roughly 1 lb (0.45 kg) per week.
• A daily deficit of around 1,000 calories is sometimes discussed in the context of losing around 2 lbs per week — though larger deficits are not appropriate for everyone and should only be pursued under clinical guidance.
• To lose 1 kg per week, a deficit of roughly 7,700 calories over the week would be required — a target that is ambitious and not suitable for most people without medical supervision.

These figures are general educational benchmarks, not personal prescriptions. Real-world results vary, and the relationship between calories and weight loss is affected by factors including metabolism, muscle mass, hormonal changes, and how much of a deficit is actually sustainable day to day.

How appetite changes on GLP-1 medication affect calorie intake

Many people already prescribed Mounjaro or Wegovy find that their appetite reduces noticeably, making it easier to eat less without feeling deprived. This is one of the commonly reported effects of GLP-1 (and, for tirzepatide, also GIP) receptor agonists acting on appetite-regulating pathways. However, eating too little — particularly too little protein — can lead to muscle loss alongside fat loss, which is why understanding your calorie and protein targets matters as much as simply reducing intake.

For a deeper look at the calorie maths behind losing a pound, see our guide on how many calories make up a pound, or explore what it takes to lose a pound in practice. If you are thinking about a larger goal, losing a stone through calorie tracking walks through how to approach that target over time.

How to figure out your personal calorie target

A personalised daily calorie target is usually calculated in two steps: first estimating your Total Daily Energy Expenditure (TDEE) — how many calories your body burns on an average day — and then applying a deficit to that number. TDEE is influenced by your Basal Metabolic Rate (BMR) plus your activity level. The calculator on this page handles that working for you. Always discuss the output with your prescriber or doctor before making significant changes to how you eat, particularly if you are on medication that affects appetite and digestion.

Knowing your calorie target is one thing — hitting it consistently is another, especially when appetite fluctuates week to week on GLP-1 medication. GLP Trackr's food logging makes staying on top of your numbers genuinely effortless: point your camera at a meal and the AI photo scan returns an instant calorie and macro breakdown, no manual entry needed. A barcode scanner and food search are there for packaged foods and anything the camera misses.

Once your daily calorie and protein targets are set inside the app, every meal you log feeds directly into your progress for the day. The insights dashboard then helps you see patterns over time — whether your intake is consistently below target, whether protein is on track, and how your food choices relate to the progress you are making on the scale.

You can also set targets for protein, water, steps, and fibre alongside calories, so the full picture of your nutrition is visible in one place rather than scattered across different tools. Pair that with the weekly transformation view and you have a clear, data-backed record to bring to your next prescriber appointment.

Browse the full suite of calorie and nutrition tools in our calorie calculator hub for more ways to understand your numbers on a GLP-1 journey.

GLP Trackr provides general informational tools to support your journey — it is not a substitute for personalised advice from your prescriber or doctor. If you are unsure what calorie intake is right for you, always check with your healthcare professional first.

Ready to put your calorie target to work? Download GLP Trackr on the App Store or Google Play and start your free 7-day trial — snap your meals, set your goals, and watch the numbers come together.