Fat Burned

Ever wonder how much fat you actually burn in a day?

FatBurn turns your Apple Health data into clear, actionable fat burn estimates — no guesswork, no calorie counting, no manual logging. Just open the app and see how much fat your body has burned today, during workouts, this week, and over your entire fitness history.

HOW IT WORKS

FatBurn uses established exercise physiology research to estimate fat oxidation from data already on your iPhone and Apple Watch:

Heart rate samples from workouts and throughout the day
Your age, weight, and biological sex from Health
Workout duration, and intensity

Calories are estimated using the Keytel formula (Keytel et al., British Journal of Sports Medicine, 2005). Fat burn is then calculated based on heart rate zone analysis — your body burns a higher percentage of fat at lower intensities and shifts toward carbohydrates at higher intensities. FatBurn classifies your effort into low, moderate, and vigorous zones and applies research-backed fat oxidation percentages to each.

WHAT YOU SEE

Daily Fat Burn — total fat burned from all activity and resting metabolism
Workout Fat Burn — fat burned specifically during recorded workouts
Weekly Trends — a 7-day chart showing daily fat burn with weekly totals
Workout Breakdown — individual workout cards with fat burn, duration, and calories
Lifetime Total — cumulative fat burned from your earliest HealthKit record
Customizable Goals — set daily, workout, and weekly fat burn targets based on CDC and AHA guidelines
All values display in grams or ounces, with support for kilograms and pounds for larger totals.

APPLE WATCH APP

FatBurn includes a full Apple Watch companion app so you can check your fat burn stats right from your wrist:

Daily and workout fat burn at a glance
Active calories, workout minutes, and weekly totals
Syncs automatically with your iPhone via HealthKit
Designed for quick, on-the-go reference

WATCH COMPLICATIONS

Add FatBurn to your watch face for instant access. Complications are available in multiple styles and sizes, showing your choice of:

Daily Fat Burn
Workout Fat Burn
Weekly Fat Burn

Choose which metric appears on your watch face from the watch app on your iPhone. Complications update throughout the day with HealthKit background delivery.

THE SCIENCE

FatBurn doesn't just make up numbers. Every calculation is grounded in peer-reviewed research:

Keytel Formula for calorie estimation from heart rate (J Sports Sci, 2005)
Achten & Jeukendrup's Maximal Fat Oxidation research (Int J Sports Med, 2003)
CDC weight loss guidelines (0.5–1.0 kg/week safe range)
AHA physical activity recommendations (150 min/week moderate exercise)
Full methodology with formulas and citations is available inside the app under Settings.

PRIVACY FIRST

Your health data stays on your device. Period.

FatBurn reads data only from Apple HealthKit on your iPhone and Apple Watch
No data is uploaded to any server — all processing happens locally
No accounts, no sign-ups, no tracking
No third-party analytics or advertising SDKs
We cannot see your health data, and we never will
FatBurn requires HealthKit access to function. You control exactly which data types you share through the standard iOS Health permissions screen.

SUBSCRIPTION

FatBurn offers a 1-week free trial with full access to all features. After the trial, continue using FatBurn for $4.99/year. No features are locked — the subscription simply lets you keep using the app you already enjoy.

1-week free trial
$4.99/year after trial (price may vary by region)
Cancel anytime — no charge if you cancel during the trial
Manage or cancel from Settings > Apple ID > Subscriptions

DISCLAIMER

FatBurn provides estimates based on published exercise physiology formulas. This app is not intended to provide medical advice. Consult a healthcare professional before making health decisions.

Terms of Use: https://www.apple.com/legal/internet-services/itunes/dev/stdeula/