How Do Apps Calculate Calories Burned?

At the core of every calorie-burn calculation is your Basal Metabolic Rate (BMR) — the energy your body uses just to keep running at rest. Apps typically derive this using established formulas (such as the Mifflin-St Jeor or Harris-Benedict equations), which take your weight, height, age, and sex as inputs. BMR is then adjusted upward based on your activity level to produce a Total Daily Energy Expenditure (TDEE) — essentially, what you burn across a full day.

How activity is measured

When you move, your phone or wearable device tracks that movement through its accelerometer (which detects motion) and, on many devices, a heart-rate sensor. The app translates raw motion data into a recognised activity type — walking, running, strength training — and applies a MET value (Metabolic Equivalent of Task). MET values represent how many times more energy a given activity burns compared with sitting still. Multiply a MET value by your body weight and the duration of the activity, and you get an estimated calorie burn for that session.

Why the numbers are estimates

No consumer app has access to a metabolic chamber, so all figures carry a margin of error. Factors that affect accuracy include how you carry your device, individual differences in muscle mass and fitness, and how well your personal stats have been entered. Think of the output as a useful guide rather than a precise reading — particularly useful for spotting trends over time.

If you want to dig further into working out your own numbers, see our guide on calculating calories burned or explore how to calculate your daily calories more broadly.

Understanding the estimate is useful — having it automatically woven into your daily picture is even more so. GLP Trackr's targets feature lets you set a daily steps goal and monitor it alongside your calorie and protein intake, so you can see your energy balance at a glance rather than juggling separate apps.

Food logging sits at the heart of that balance. Snap a photo of a meal and the app's AI scan returns an instant calorie and macro breakdown — useful on a GLP-1 journey when appetite fluctuates and portion sizes shift week to week. You can also use the barcode scanner or manual search if a photo scan isn't convenient. Pair that with your steps data and you have a complete, real-world picture of intake versus output to take to your next prescriber appointment.

For a fuller view of your progress over time — including whether your activity patterns are shifting as your dose changes — the insights and analytics section surfaces correlations across your logged data. You can explore how steps, food intake, and weight interact across your journey, which is the kind of context that a simple calorie-burn number on its own can't provide.

Head to our calorie calculator hub for more tools to support your tracking, and if you're thinking about how weight loss itself is measured, our page on calculating percentage weight loss is a useful companion.

GLP Trackr is a tracking tool, not a clinical service — always follow the guidance of your prescriber or doctor when it comes to your health goals and any changes to your routine.

Ready to bring activity, food, and weight data together in one place? GLP Trackr is free to try for 7 days — available now on the App Store and Google Play.