How to Calculate Calories Burned — and Why It Matters on a GLP-1 Journey

Your total daily energy expenditure (TDEE) — the standard way of estimating calories burned — is made up of several components working together:

• Basal metabolic rate (BMR): The calories your body burns simply keeping you alive — breathing, circulation, cell repair. This is the largest component for most people.
• Physical activity: Movement of any kind, from a brisk walk to a gym session. This is the most variable part of the equation.
• Thermic effect of food (TEF): The energy it takes to digest and process what you eat — typically around 10% of calorie intake, though this varies.
• Non-exercise activity thermogenesis (NEAT): The calories burned through everyday movement that isn't formal exercise — fidgeting, standing, walking between rooms.

Common formulas used to estimate BMR

Two equations are frequently used as starting points. The Mifflin-St Jeor equation is widely considered one of the more reliable for general use, factoring in weight, height, age, and biological sex. The Harris-Benedict equation is an older alternative that works similarly. Both give an estimate — not a definitive figure — because individual metabolism varies considerably.

Why GLP-1 medicines can change the picture

People taking Mounjaro (tirzepatide) or Wegovy (semaglutide) often experience reduced appetite and eat significantly less than before. This can affect the thermic effect of food and, over time, body composition — which in turn affects BMR. It's one reason that tracking your numbers over weeks, rather than relying on a single calculation, tends to give a more useful view of where you are. For more on understanding your overall energy needs, see our guide on how to calculate calories and the broader context in our calorie calculator hub.

Activity multipliers — a rough guide

Once you have a BMR estimate, multiplying it by an activity factor gives a TDEE approximation. Common multipliers range from around 1.2 (largely sedentary) to 1.9 (very physically active). These are general starting points; what matters most is consistency — using the same approach over time so you can spot trends rather than chasing an exact number.

Manually running equations each day is useful once; doing it repeatedly is where most people lose momentum. GLP Trackr's targets feature lets you set a daily calorie goal based on your own numbers, and the app tracks your progress against it throughout the day — so the maths stays in the background where it belongs.

Paired with AI photo food logging — point your camera at a meal and get an instant calorie and macronutrient breakdown — you get both sides of the energy balance in one place: what you're consuming and what you're aiming for. For people on GLP-1 medicines who are eating smaller, less predictable amounts, this kind of effortless logging makes it far easier to stay consistent without obsessing over every bite.

You can also log your daily step count, which feeds into your activity picture over time. The insights dashboard then surfaces patterns — for example, whether the weeks you hit your step target tend to coincide with better progress — giving you something concrete to discuss at your next prescriber appointment.

Curious about how apps arrive at these figures in the first place? Our page on how fitness apps calculate calories burned goes deeper on the methodology, and our comparison of the best apps to calculate calories puts the options in context.

GLP Trackr is free to try for 7 days — available on the App Store and Google Play. Set your targets, snap your meals, and let the app keep score while you focus on the journey.