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When you first open Fat Burn, you'll be prompted to grant HealthKit access. You can also manage permissions in iOS Settings > Privacy & Security > Health > Fat Burn.
Make sure you've granted HealthKit permissions and that you have workout or health data recorded. The app needs data from Apple Health to display fat burn metrics. Workout fat burn requires recorded workouts with heart rate data.
Fat burn is estimated using the Keytel formula for calories per minute (based on heart rate, weight, age, and sex), combined with heart rate zone-based fat percentages: Low (<100 bpm) = 65% fat, Moderate (100–119 bpm) = 50% fat, Vigorous (≥120 bpm) = 35% fat. Fat grams = (calories × fat%) ÷ 9 cal/g ÷ 2.
In the Settings section of the app, you'll find a "Display Unit" picker. Tap Grams or Ounces to switch. For large values (like lifetime totals), the app automatically displays in kg or lbs.
Long-press on your Apple Watch face, tap Edit, and scroll to find Fat Burn complications. Choose from circular, corner, rectangular, or inline formats showing your fat burn data.
No. All your health data stays on your device. We never transmit or store your HealthKit data on external servers. Data is only shared between your iPhone and Watch via a secure App Group.
Fat Burn Pro is an optional annual subscription ($4.99/year) that unlocks full analytics and Apple Watch companion app features. You can manage your subscription in Settings or through the App Store.
Simply delete the Fat Burn app to remove all locally stored app data. Your HealthKit data remains in Apple Health and is managed by iOS.
Fat Burn is not a medical device and does not provide medical advice, diagnosis, or treatment. All data displayed — including fat burn estimates, calorie figures, and heart rate zone analysis — is for informational and personal fitness tracking purposes only. Do not use this app to make medical or health decisions. Always consult your physician or qualified healthcare provider with any questions about a medical condition or fitness program.