Burn
Get Burn
Burn
Get Burn
Start the timer and Burn shows you the stage your body is in, hour by hour. When hour 14 hits and you want to quit, it hands you something to do about it.
iPhone and Apple Watch. Nothing to weigh, nothing to photograph.
Fed State through Deep Autophagy. Each one tells you what's happening in your body right now, and how sure anyone actually is about it.
Six tools, one tap away, for when hunger spikes: a timer that outlasts the craving, water first, a symptom check, your own reason.
No calorie database. No photographing dinner. No macros. One question: when did you stop eating?
The nine stages
Hour 8 is not hour 16. Your body burns through stored sugar first, then starts pulling from fat, then shifts again. Burn names the stage you're in and what usually comes next, so you always know where you are.
And you get both views. The top rail is the model in the app. The bottom rail is what the research supports: soft, overlapping, no exact switch-on. No other timer shows you that.
Inside the stages
On a 16:8 you will pass through these three, in this order, every single day. Tap any stage in the app and you get the same thing: what your body is doing, what you might feel, and what comes next.
What's happening
Liver glycogen stores are running low. The body begins gluconeogenesis, manufacturing glucose from lactate, glycerol and amino acids. Hunger signals may increase. This is temporary and will pass.
You may feel
Increased hunger, possible irritability, difficulty concentrating. This is the hardest window for most people.
Next up: Fat Mobilisation
What's happening
Insulin is now low enough that stored body fat begins to be released into the bloodstream as free fatty acids. The liver starts converting these into ketone bodies. You are transitioning into fat-burning mode.
You may feel
Hunger may intensify briefly, then begin to fade. Light-headedness is possible, so stay hydrated.
Next up: Ketosis Entry
What's happening
Ketone production is meaningful. The brain begins supplementing its glucose use with ketones. Many people experience a mental clarity shift at this stage. Hunger often subsides.
You may feel
A shift in mental clarity. Hunger often drops noticeably. Some experience a mild euphoria.
Next up: Fat Burning
All nine stages carry this detail, and each one says how firm the evidence behind it is. See all nine stages →
When it gets hard
Hunger isn't a line that keeps climbing. It comes in waves that peak and pass, whether you eat or not. Wait out the wave and it's gone.
So hit I'm struggling and Burn starts a 20-minute hunger timer right on your home screen, next to your water count and your reason for doing this. Five more tools behind it if that one doesn't land.
6
tools, one tap away
20:00
the wave you have to outlast
0
food photos to log
Proof you're getting somewhere
Which day you fast longest. What your streak is worth. Whether the scale is really moving or just bouncing. Burn does the arithmetic and shows its work. If it needs data you haven't given it, it says so instead of guessing.
"Wednesday is your power day. 18.3h average, 2.5h ahead of Monday." Five new reads like that, every week.
Every fast by day, week and month. Hours, energy, mood, water and weight, in one place you can actually scroll back through.
A two-minute read waiting for you at 04:08, written from your own numbers, with 6 citations attached.
Schedules
Dinner at 8pm, lunch the next day. Six moments from the same fast. This is what you'd actually watch happen on your phone.
02h 14m
Fed State
05h 08m
Early Fasting
08h 41m
Glycogen Depletion
12h 17m
Glycogen Depletion
14h 36m
Fat Mobilisation
16h 22m
Goal met
Fat Mobilisation appears as FAT RELEASE on the timer screen, where space is tight. Same stage, shorter name.
Guided programs
Pick the goal. Burn writes the week. A target for every day, easier on weekends, harder when you're ready for it.
Four weeks that climb from 16h to 24h and back down. For people who've fasted before and stalled.
A steady 16h Monday to Friday, loose on weekends. Built around a workday, not a retreat.
Alternating lengths that flatten the blood-sugar swings behind the 3pm crash. One week, beginner-friendly.
Every day you complete gets ticked off. Miss one and nothing collapses. The week rolls on, and Burn adjusts what it asks of you next.
11
days done
17
remaining
39%
complete
Body Score & streaks
Fasting, hydration and consistency, scored out of 100. It shows you exactly which part is dragging, so you know what to fix tomorrow.
Streaks work the way they should: 2 freezes a month, used automatically. One bad Tuesday doesn't wipe out ten weeks.
61
day streak
12
records to beat
5
challenges to enter
On your wrist
Start a fast, log water and end it without reaching for your phone. The stage name sits under the clock, and the ring changes color as you cross each one.
Your Body Score, water and streak are one swipe away.
See Burn on Apple Watch →
Native iOS and watchOS. A buzz on your wrist when you cross into a new stage. Apple Health if you want it, nothing collected that the app doesn't use, and your data leaves whenever you ask.
Start at 12:12 and work up. Or take a guided program built around your goal: fat loss, focus, energy, or a full metabolic reset. Burn sets each day's target for you.
21 guided programs, 7 quick plans from 11:13 to alternate-day, and 3 custom protocols of your own.
See all the plans →GUIDE · 3 MIN
Hunger waves, ghrelin timing, and the twenty minutes that decide most fasts.
SCIENCE · 3 MIN
What is measured in humans, what is measured in mice, and what is still an inference.
GUIDE · 3 MIN
Black coffee, electrolytes, and the gray areas where the debate actually lives.
SAFETY · 3 MIN
Pregnancy, eating-disorder history, medication, and the symptoms that mean stop.
Pro tells you when you fast best, how deep you actually get, and mails you a monthly report you can hand to anyone.
Finish dinner, hit start, go to bed. You'll wake up eight hours in with most of the work already done. The stages, the struggle tools and the whole library are all in the app.
iPhone, iPad, and Apple Watch. Requires iOS 18 or watchOS 11.