Calorie Deficit Calculator: Understand Your Numbers on a GLP-1 Journey

Your calorie deficit is simply the gap between the calories your body needs to maintain its current weight (your Total Daily Energy Expenditure, or TDEE) and the calories you actually consume. When that gap is consistent over time, your body draws on stored energy — which is why tracking it matters.

How the calculation works

The calculator uses your height, weight, age, and activity level to estimate your TDEE, then subtracts a target deficit to give you a daily calorie goal. General educational guidance — broadly in line with public health information — typically places a sensible deficit somewhere between 300 and 700 calories per day. Going too far below your TDEE can lead to fatigue, muscle loss, and difficulty sustaining the approach, so the number is a starting point for a conversation with your prescriber or doctor, not a rigid instruction.

Why this matters on a GLP-1 medicine

GLP-1 medicines like Mounjaro (tirzepatide) and Wegovy (semaglutide) commonly reduce appetite and food noise, which means many people naturally eat less without counting every calorie. Even so, knowing your rough deficit helps you stay in a productive range — especially on days when appetite reduction is stronger and you might inadvertently eat too little protein or total energy to support your goals.

For a straightforward starting-point estimate, you can also explore our general calorie deficit calculator or the free calorie deficit calculator for additional tools. If you are specifically looking at how national health guidance frames these numbers, our page on the NHS-aligned calorie deficit approach covers that context in more detail.

What affects your result

• Activity level: a more active day raises your TDEE, meaning you can eat more and still maintain the same deficit.
• Body composition: muscle burns more energy at rest than fat, so two people with the same weight may have different TDEEs.
• Rate of progress: a larger deficit produces faster results on paper, but may be harder to sustain — particularly alongside GI side effects that are common early in treatment.

Always treat any calculated figure as an educational estimate. Your prescriber or doctor is best placed to advise on the right calorie target for your specific health situation.

Calculating your deficit once is useful — logging it every day is where the real insight comes from. GLP Trackr's food logging feature is built to make this effortless on a GLP-1 journey, when appetite shifts and portion sizes change week to week.

Point, snap, done

The AI photo-scan feature lets you photograph a meal and get an instant breakdown of calories, protein, and macros — no manual entry needed. On days when appetite is low and meals are small, this means you can log accurately without it feeling like extra effort. A barcode scanner and manual search are there for everything else.

Set your target, watch the gap

Once you have your deficit figure from the calculator above, you can set it as your daily calorie target inside the app. GLP Trackr then tracks your intake against that target in real time, so you can see your deficit close — or confirm you are staying within a healthy range — without any mental arithmetic.

The daily check-in also captures weight, mood, energy, and food noise alongside your nutrition data, so you can start to see how your deficit interacts with how you actually feel. That kind of pattern — available in the app's insights view — is genuinely useful to bring to appointments with your prescriber.

For a fuller view of all the tracking tools available, visit our calorie calculator hub.

GLP Trackr is free to try for 7 days on the App Store and Google Play — no commitment needed to see whether the daily calorie tracking fits your routine.

The calorie targets this calculator produces are general educational estimates. They are not a substitute for personalised advice from your prescriber or doctor, who can take your full medical history into account.