How to Calculate a Calorie Deficit on Your GLP-1 Journey

Calculating a calorie deficit starts with knowing your Total Daily Energy Expenditure (TDEE) — the number of calories your body uses on an average day. Once you have that figure, a deficit is simply any daily intake below it.

Step 1: Estimate your Basal Metabolic Rate (BMR)

Your BMR is the calories your body needs at complete rest just to keep basic functions running. It is influenced by your age, sex, height, and weight. A widely used formula is the Mifflin-St Jeor equation, which generally gives a reasonable starting estimate for most adults. You can use our calorie calculator hub to run this automatically.

Step 2: Factor in your activity level

Multiply your BMR by an activity factor — typically ranging from around 1.2 (mostly sedentary) to 1.7 or higher (very active). The result is your approximate daily maintenance calorie need. This is the number you are trying to go below to create a deficit.

Step 3: Decide on a modest deficit

A commonly cited general range for a sustainable deficit is roughly 300–500 calories below maintenance per day. This is educational context, not a personal prescription — the right deficit for you depends on factors your prescriber or doctor knows about your health history. Larger deficits are not necessarily better and can lead to muscle loss or fatigue, which matters especially on a GLP-1 medicine where protein intake already needs attention. For practical guidance on setting your daily intake figure, see how to calculate your calorie intake.

What about calorie maintenance specifically?

Learning how to calculate calorie maintenance — your break-even number — is just as valuable as finding your deficit. If weight loss has stalled, checking whether your actual intake has crept back up to maintenance (or above) is a logical first step. You can explore the relationship between these numbers and your results in more detail on the page covering calculating expected weight loss.

Keep in mind that TDEE formulas are estimates. Real-world factors — stress, sleep quality, hormonal changes, and the slowed gastric emptying commonly associated with GLP-1 medicines — all affect how your body uses energy in practice.

Knowing the formula is one thing; actually hitting your numbers day after day is where most people find it hard — especially when appetite is unpredictable on a GLP-1 medicine. GLP Trackr is built to make this effortless.

The most relevant feature here is AI photo food logging: point your camera at a meal and the app estimates calories, protein, and macros instantly — no manual searching required. On days when food noise is low and portions are small, this takes almost no effort at all.

From there, your personalised calorie and protein targets sit in the app alongside your food log, so you can see your running deficit in real time rather than guessing. If you prefer to set targets based on a calculation you have already worked out, you can enter them directly. For a dedicated tool to help you find your numbers, the GLP Trackr calorie deficit calculator walks through the steps with you inside the app.

The daily check-in adds context too — logging your weight, energy, and sleep alongside your food data means you can start to see how your deficit is (or isn't) translating into progress over time, and spot patterns worth discussing with your prescriber.

Any calorie targets you set should reflect guidance from your prescriber or doctor — they understand your full clinical picture, and no calculator replaces that conversation.

Ready to stop estimating and start tracking? Download GLP Trackr on the App Store or Google Play and explore every feature free for your first 7 days.