choose a goal below
Fasting goal — build up gradually
Hydration
Water today
◗ time for a sip0.0 / 3.0 L
no water logged yet
Water is the one thing to stay on top of every fasting hour. On longer fasts your body also loses sodium, potassium and magnesium — see the guide tab.
What happens inside
The metabolic journey
Your progress
Streak & history
0
Day streak
0h
Longest fast
0
Fasts done
Stay safe · stay motivated
Fasting, done well
Track these five things ›
- Time since eating — the clock on the Fast tab. Note when you actually finished your last meal (tap “Adjust start time”).
- Water — sip steadily; pale-yellow urine is the target. Don't wait until you're thirsty.
- Electrolytes — on fasts past ~16–18h, add a little salt; consider potassium & magnesium too. They carry no calories and won't break the fast.
- How you feel — steady energy, clear head, mild hunger waves are normal. Dizziness, a racing heart, or confusion are not.
- The re-feed — break the fast gently. Start small (broth, a little protein or fruit), then a proper meal. The longer the fast, the gentler the return.
Building up to longer fasts ›
Treat this like training, not a test of willpower. A sensible ladder: get comfortable at 13h, then 16h, then 18h. Hold each rung for a week or two before adding the next. Most people do best with regular 16–20h fasts, and an occasional 24–36h fast once or twice a month for the deeper autophagy benefits. Only step into multi-day territory once shorter fasts feel genuinely easy — and with a doctor's blessing.
Before you fast — the honest bit ›
This is a tracker, not medical advice. Talk to a doctor first — especially before any fast longer than 24 hours. Fasting is not suitable if you are pregnant or breastfeeding, under 18, have a history of an eating disorder, have type 1 diabetes or take insulin or blood-sugar / blood-pressure medication, or have kidney disease or are underweight. Stop and eat if you feel faint, get heart palpitations, feel confused, or become severely weak.
The science here reflects a typical healthy adult; individual timing varies with your last meal, activity and metabolic health. Grounded in research featured in the documentary “Fasting: Awakening the Rejuvenation from Within” (Gilman & de Lestrade) and current work on ketosis and autophagy.
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works offline · no account · your data never leaves your phone