Calorie Deficit Calculator: What It Is and How to Use It on Your GLP-1 Journey

Your body burns a certain number of calories every day just to keep you alive and moving — this is often called your Total Daily Energy Expenditure (TDEE). A calorie deficit is created when you eat less than that number. A modest, sustainable deficit — commonly described in general nutrition guidance as around 500 calories below your TDEE — is typically associated with gradual, steady weight change, though individual results vary considerably.

Why This Matters Differently on a GLP-1 Medicine

GLP-1 receptor agonists like semaglutide (Wegovy) and tirzepatide (Mounjaro) work in part by reducing appetite and increasing the feeling of fullness, which means many people naturally eat less without trying to count calories at all. This is helpful, but it also creates a risk of eating too little — particularly of protein, which is important for preserving muscle while losing weight.

Knowing your approximate calorie needs gives you a useful reference point: not a rigid target to hit every day, but a range that helps you stay nourished. General guidance from nutrition organisations typically suggests that intakes below around 1,200 calories per day for women or 1,500 for men should only be followed under clinical supervision — but always discuss your specific situation with your prescriber or doctor rather than applying any general figure as a personal rule.

What Goes Into the Calculation

A calorie deficit calculator typically takes into account your:

• Current weight and height
• Age and sex
• Activity level (sedentary, lightly active, moderately active, very active)
• Your goal (rate of weight change)

These inputs produce an estimated TDEE and a suggested deficit range. Because they are estimates based on population averages, treat the output as a starting point rather than a precise prescription.

If you want to explore the numbers in more depth, our calorie deficit calculator walks you through the calculation step by step, and the extended deficit calculator lets you adjust activity levels and goals in more detail. You can also try the free calorie deficit calculator for a quick, no-signup estimate. All of these sit within the broader calorie calculator hub, which covers related calculations including protein and TDEE.

Calculating a deficit is the easy part — hitting it consistently while appetite fluctuates on a GLP-1 medicine is where most people find tracking genuinely useful. GLP Trackr's AI food logging makes this as frictionless as possible: point your camera at a meal and the app estimates the calories, protein, and macros instantly, without manual entry.

Once you have a calorie target in mind — whether from the calculator above or agreed with your prescriber — you can set it directly inside the app. GLP Trackr then tracks your intake against that target each day, so you can see at a glance whether you are in a meaningful deficit, eating roughly at maintenance, or dipping too low. The daily check-in also captures weight, energy, and mood alongside your food data, which means you can spot patterns over time: for example, whether the days you eat more protein correlate with better energy or fewer side effects.

This kind of joined-up data is genuinely useful to bring to your prescriber appointments too — the app can generate a summary of your journey to share with your healthcare team.

A note worth keeping in mind: calorie calculators give estimates, not prescriptions. If you are losing weight faster than expected, feeling very fatigued, or concerned about how much you are eating, talk to your prescriber or doctor — they can help you find a level that is right for your body and your stage of treatment.

Ready to put the numbers to work? Download GLP Trackr on the App Store or Google Play and start a free 7-day trial — snap your first meal, set your calorie goal, and let the app do the tracking from there.