The Best App to Calculate Your Calorie Deficit on Mounjaro or Wegovy

A calorie deficit occurs when the calories you eat and drink in a day fall below the number your body burns at rest and through activity. Over time, a consistent deficit is what drives body-fat reduction. The size of a sustainable deficit varies from person to person — factors like starting weight, height, age, sex, and activity level all influence your total daily energy expenditure (TDEE), which is the baseline the deficit is measured against.

Why tracking matters more than estimating

On a GLP-1 medicine such as tirzepatide (Mounjaro) or semaglutide (Wegovy), appetite often reduces noticeably — something many people describe as a quietening of food noise. While that can feel like progress, it can also mean eating very little without realising it, making it harder to hit adequate protein targets or stay within a healthy range. Tracking your actual intake against your estimated TDEE reveals whether your deficit is appropriately sized or has crept too low.

How deficit calculators work

Most calorie-deficit calculators use a recognised formula — such as the Mifflin-St Jeor or Harris-Benedict equation — to estimate your basal metabolic rate (BMR), then apply an activity multiplier to arrive at your TDEE. Subtracting your logged food intake from that figure gives your estimated daily deficit. These are estimates rather than precise measurements, but consistent tracking over days and weeks makes the numbers progressively more meaningful. For a deeper look at working out your intake target, see our guide on how to calculate calorie intake.

If you want to go further and explore the numbers in detail, our dedicated calorie deficit calculator walks through the calculation step by step. You can also find the broader calorie-tracking toolkit on the calorie calculator hub.

GLP Trackr is built specifically for people on Mounjaro and Wegovy, and its food-logging features are designed around the realities of GLP-1 life — smaller meals, shifting appetite, and a genuine need to hit protein goals even when hunger is low.

AI photo scan and barcode logging

The fastest way to log food in GLP Trackr is to point your phone camera at your meal. The AI photo scan identifies what is on the plate and returns an instant calorie and macro breakdown — no manual searching needed. For packaged foods, the barcode scanner pulls nutritional data in seconds. Both methods feed directly into your daily calorie total, so your deficit is calculated for you in real time without manual arithmetic.

Targets and daily insights

Once you set your calorie and protein targets inside the app, GLP Trackr tracks your running intake throughout the day and shows clearly how far you are from your goal. The daily brief and week-at-a-glance insights let you see patterns — whether you are consistently hitting your deficit, whether protein is falling short, or whether low-intake days are clustering in a way worth discussing with your prescriber. For guidance on choosing the right figures to enter, our page on tracking calories on a GLP-1 covers what to consider.

General educational guidance suggests many adults aim for a moderate, sustainable deficit rather than a very steep one, but the right target for you depends on your individual circumstances. Always follow the personalised guidance from your prescriber or doctor — they know your full health picture and can advise on appropriate nutrition targets alongside your medication.

Ready to stop estimating and start seeing your deficit clearly? Download GLP Trackr on the App Store or Google Play and explore every feature free for 7 days — no guesswork, just your own data working for you.