Questions, answered

iPhone, iPad, and Apple Watch. Burn requires iOS 18 or watchOS 11.

Download free on the App Store. Set your schedule, start your first fast, and the timer runs from there.

Nine, starting at 11:13 and running up through 14:10, 16:8, 18:6 and 20:4 to OMAD. You can also run a flexible fast with no set end time. Compare all nine.

A Burn product score out of 100 that reads your own day. Fasting, Hydration and Consistency come from what you log in Burn. Connect Apple Health and Sleep and Activity join, covering all five parts. It is not a health or metabolic measurement. How it is built.

No. Morning Brief assembles what Burn already knows about your night and your recent fasts into one screen you read before deciding how long to go. It is not a diagnosis or a medical assessment. See Morning Brief.

Burn records the fast at the length you actually reached, along with the stage you got to. Streak Freezes cover the days life gets in the way, so one short fast does not erase weeks of work.

Start shorter than you think you need. 14:10 is a good first target because it fits a normal day and still reaches the start of Fat Mobilisation. Move up when the current length stops taking effort. The beginner guide.

Water, plain black coffee, plain tea, salt, and electrolytes without calories. Anything with meaningful calories ends the fast, including milk in your coffee. The full list.

Hunger arrives in waves that peak and pass rather than climbing steadily. The wave typically lands well before the end of a 16 hour fast. Burn's Struggle Support gives you six tools for exactly that hour. Hunger while fasting.

Easy and moderate work usually goes fine. Hard intervals and heavy lifting want glycogen, so those sit better inside your eating window. Fasting and exercise.

Usually sodium rather than the fast itself. Lower insulin tells your kidneys to release sodium and water, and plain water alone can make it worse. Electrolytes while fasting.

No. Burn maps elapsed time to named stages. It does not measure ketosis, autophagy, or metabolic state. A blood or breath test is what gives you an actual ketone number, and you can store your own readings in Burn's Journal.

The clock is exact. The biology varies with your last meal, your activity, your sleep and your metabolism, so Burn draws each line where a timer has to draw one and describes the stage in terms of what is likely. You get both views. All nine stages.

Fat use rises gradually rather than switching on. Burn names Fat Mobilisation at 14 hours, Ketosis Entry at 18, and Fat Burning at 24. The fuel sequence.

Much of the work on autophagy comes from animal models, and human trials on its timing and scale are active research areas. Burn describes it as research rather than an outcome you have achieved. Autophagy and fasting.

Speak to a doctor before starting if you are pregnant or breastfeeding, have a history of eating disorders, manage diabetes, take medication timed to meals, or are under 18.

Stop and eat if you feel unwell, whatever the timer says. Dizziness that does not settle, heart palpitations or shaking are a different category from ordinary hunger, and are worth raising with a doctor if they repeat.

No. Burn is a fasting timer. It does not diagnose or treat anything, and nothing in the app or on this site replaces advice from your own doctor.