Tool
Fasting phase calculator
Enter when you started your fast — or how many hours you're in — and see which biological phase you're in right now, plus how long until ketosis and autophagy.
Enter a start time or hours elapsed to see your current phase.
Fed state
Hour 0
Digestion & nutrient storage
Until ketosis · 16h
—
Until autophagy · 24h
—
Phase timings are a well-supported approximation, not a precise clock — your last meal, activity, and metabolism shift the exact hour. Not medical advice.
When will I reach ketosis?
Ketosis usually begins around hour 16, when liver glycogen has run low and the liver starts producing ketone bodies the brain can use. Autophagy — the cell's recycling program — picks up after about hour 24. These are the same boundaries the app's phase-aware timer uses.
For the full hour-by-hour walk through all six phases — fed state, early fasting, lipolysis, ketosis, autophagy, and the deep fast — with the biology and primary sources cited inline, read the fasting timeline pillar.
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Try the app
Intermittent tracks this in real time.
Free on Android and iOS — phase-aware timer, the full library, and no paywall. The biology you just read about, live on your home screen.