Basics · Updated Sep 30, 2026 · 8 min read
Open-ended & multi-day fasts
Why this timer has no finish time you must pay to pass, how a stretch of one to three days differs from a daily window, and why the clock can follow a plan you already have.
Fasting Fundamentals · Part 9 of 12 · Fasting Library
Some fasting apps stop at a daily window, or charge to keep counting past it. On this timer, Open has no finish time. It counts until you press End Fast. You can still pick 16 hours, 24 hours, or a custom goal when you want the ring to fill. A religious calendar, a trip, or a plan you already made can sit outside a neat 16-hour day, and the clock can follow that day.
The missing cap is there so the clock can match a plan. More hours are not a healthier result, and they are not a larger dose of autophagy. Autophagy is a recycling process inside cells, and the timer cannot measure it. Autophagy: what headlines get wrong separates that word from the clock. A stretch of one to three days without food also carries more risk than eating every day. If that stretch is what you mean, talk with a clinician who knows you before you start.
What Open does
Open keeps counting with no target hour and no payment to continue. The other hour buttons, including 24h, 36h, and 48h, are listed in Presets on this clock. You can run with a goal, or with none.
Names such as Ketosis and Autophagy Window change as the hours pass. They follow the clock. They are not a lab result, and Autophagy Window is not a finish line you are supposed to reach. What those names are for is in What the stages on the timer mean.
You can press End Fast at any time. On a long session, that button matters more than the number on the screen.
One to three days is not two daily windows
A daily window still includes food every day. A 36, 48, or 72 hour stretch does not. Sleep, medicines, what you drink, and the first meals afterward all change. Water and salt on that stretch are in Water and minerals past a day. How you eat again is in Breaking a fast gently.
Human trials of fasts that last a full day or longer are fewer and smaller than the daily-window trials, and many of them are supervised. A 72-hour button is not those papers. A water fast in a video, or a badge in another app, is a weak reason to skip food for three days at home.
Long fasts in nineteenth- and twentieth-century clinics were supervised treatments. Copying the hours at home skips the person who was there to stop them. If you do not already have a clinician who knows you, do not start with a multi-day target.
These buttons are not where you start
Pregnancy, an eating-disorder history, being under 18, and several medicines are reasons to stay off 36h, 48h, and Open until a clinician has said otherwise. Those situations are listed in Who should be careful with fasting. The long buttons exist so someone who already has a plan can time it. They are not the step after a first 16:8.
If you are new to this, start near the overnight gap you already have. The first day of that is in How to start fasting. If you already mean a stretch past a day, the preparation is in Before a longer fast.
If you feel worse as the hours add up, including dizziness, confusion, chest pain, fainting, or weakness you cannot explain, stop. Eat, if you can do that safely, and get help. Those signs are written out in When to stop a fast. A stage name is not a reason to keep going through them.
Say the plan before you press Start
Before you press Start, say why this length, the time you will stop even if you feel all right, and the person you will tell. A plan you can say in one sentence is easier to keep than a mood on the morning you begin.
Keep water nearby, and keep a way to eat if you need to stop. Do not add a sauna, a hard workout, or alcohol as an extra test on the same day.
The history list is a record of your fasts. It is not a ranking, and this timer will not score your hours against anyone else.
Past 72 hours, the risks are a different size again. If you have already chosen a stretch that long, read If you already mean many days before you treat Open as a way to keep going for a week.
Key takeaways
- Open has no finish time. It counts until you press End Fast, so the clock can follow a plan you already have. More hours are not a better result.
- A 36, 48, or 72 hour stretch skips food for more than a day. That is a different practice from a daily window, with different risks.
- Ketosis and Autophagy Window follow the hours. They are not lab results, and they are not a finish line.
- 36h, 48h, and Open are not the next step after a first 16:8. If you are new, start near the overnight gap you already have.
- Stop and eat if you feel seriously unwell. A headline or a clinic story is a weak reason to start a multi-day fast at home.
Educational only. Not medical advice. See our disclaimer.