Track Every Gram of Fat You Burn
Workout · Daily · Weekly · Lifetime — in grams, ounces, kg, or lbs
Fat Burn tracks fat burned across workouts, daily activity, the full week, and your entire HealthKit history — all with heart rate zone analysis and the peer-reviewed Keytel formula. Beautiful radial gauges on iPhone. Real-time complications on Apple Watch. Your data never leaves your device.
Four Dimensions of Fat Burn
Fat Burn doesn't just show total calories — it shows the fat-specific portion you're burning, across every time scale that matters.
Workout Fat Burn
During workouts, Fat Burn analyzes your heart rate minute by minute and classifies each into low, moderate, or vigorous intensity zones. Each zone burns a different percentage of calories from fat — giving you a scientifically grounded fat burn estimate for every exercise session.
- Per-workout fat burn in grams or ounces
- Heart rate zone classification (65% / 50% / 35% fat)
- Keytel formula calorie estimation
- Fallback estimation from HealthKit active calories when no HR data
Daily, Weekly & Lifetime
Daily fat burn combines active and basal metabolism — approximately 55% of total daily calories come from fat oxidation. Weekly aggregation shows your Monday–Sunday totals. Lifetime sums all HealthKit history from your earliest record, automatically displayed in kg or lbs when the numbers get large.
- Daily fat burn = (Active Cal + Basal Cal) × 55% ÷ 9
- Weekly bar chart with workout + total fat per day
- Lifetime fat burn hero banner — auto upgrades to kg/lbs
- Adjustable goals for daily, workout, and weekly targets
Everything You Need to Track Fat Burn
Workout breakdowns, radial gauges, Apple Watch complications, unit switching, and complete privacy.
Daily Fat Burn
See total fat burned throughout the day from both active movement and resting metabolism — displayed in grams or ounces, with automatic upgrade to kg or lbs for large amounts.
Workout Fat Burn
Get per-workout fat burn breakdowns using heart rate zone analysis. See exactly how much fat you burned in each exercise session — not just total calories, but the fat-specific portion.
Weekly Fat Burn
Aggregate your fat burn across the full week (Monday–Sunday) with a visual bar chart. See both workout fat and total fat side by side to track your weekly progress.
Lifetime Fat Burn
Track your all-time fat burn from the earliest HealthKit data on your device. See your cumulative progress in kg or lbs — a powerful motivator for long-term fitness goals.
Apple Watch Complications
Dedicated watch face complications for fat burn in circular, corner, rectangular, and inline formats. See your metrics at a glance with automatic background refresh every 15 minutes.
Beautiful Gauge Dashboard
Polished radial gauges for daily and workout fat burn, with supporting mini-stat gauges for active calories, total calories, workout minutes, and weekly fat — all on one beautiful screen.
Grams & Ounces (kg & lbs)
Switch between grams and ounces anytime. Large values automatically display as kilograms or pounds for easy reading. Adjustable goals for daily, workout, and weekly fat burn.
Privacy First
All data stays on your device. No cloud uploads, no accounts, no third-party analytics. Your health data is yours alone.
Your Health Data Stays With You
Fat Burn stores all health data locally on your device. No cloud uploads, no accounts, no third-party analytics, no tracking. Your fat burn data, workout history, and lifetime metrics are truly private.
Frequently Asked Questions
How does Fat Burn calculate fat burned during workouts?
Fat Burn uses heart rate data from Apple Health to classify each minute into low, moderate, or vigorous intensity zones. Each zone has a different fat oxidation percentage (65%, 50%, or 35%). Combined with the Keytel formula for per-minute calorie estimation, this gives you an accurate workout fat burn in grams or ounces.
What units does Fat Burn support?
Fat Burn displays fat burned in grams or ounces — switch anytime in settings. For larger amounts (like weekly or lifetime totals), the app automatically upgrades to kilograms (kg) or pounds (lbs) for easier reading.
What is the Keytel formula?
The Keytel formula (Keytel et al., British Journal of Sports Medicine, 2005) estimates calories per minute from heart rate, body weight, age, and biological sex. It's a peer-reviewed, scientifically validated method used for exercise physiology research and fat burn estimation.
Can I see fat burn on my Apple Watch face?
Yes. Fat Burn provides dedicated Apple Watch complications in circular, corner, rectangular, and inline formats. Your fat burn data updates automatically via background refresh every 15 minutes.
Does Fat Burn work without an Apple Watch?
Yes. The iPhone app works independently with Apple Health data, displaying your full gauge dashboard with daily, workout, weekly, and lifetime fat burn. The Apple Watch companion adds real-time watch face complications.
How is daily fat burn calculated?
Daily fat burn includes both active calories (from movement and workouts) and basal calories (resting metabolism). The formula is: (Active Cal + Basal Cal) × 55% ÷ 9 cal/g. The 55% represents the average proportion of daily energy from fat metabolism; 9 is the caloric density of fat per gram.
* Fat burn estimates are based on established exercise physiology formulas. Actual fat oxidation varies with diet composition, fitness level, genetics, and individual metabolism.
Medical Disclaimer: 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.