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Fasting calculator
When does your eating window open? Enter when your fast starts and pick a schedule.
In short: The fasting calculator shows when your eating window opens and closes, for 16:8, 18:6, 20:4, OMAD and more. Fasting time is real, elapsed time from when your fast starts, calculated in your browser's time zone. What this page says about intermittent fasting comes from the German Nutrition Society (DGE).
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Your eating window
Calculating …
Add to calendar
One event per eating window, from the chosen day. The file is created in your browser and opens in Apple Calendar, Google Calendar or Outlook.
Everything is calculated in your browser. Nothing you enter is sent or stored.
Before you fast
With diabetes, insulin, SGLT2 inhibitors, gout, pregnancy, an eating disorder, or under 18: fast only under medical supervision.
Spotting low blood sugar. Trembling, sweating, a racing heart, confusion, or vision problems while fasting can be signs of low blood sugar. Break the fast then and eat something rich in carbohydrates. If you take insulin or blood-sugar-lowering medication, fast only under medical supervision.
How the calculator works
- Fasting time is real, elapsed time: 16:8 means 16 hours without food, then the eating window opens.
- Your fast starts at the same clock time every day. The eating window closes when the next fast begins the following day.
- If the clocks change overnight, the fast stays the same length. The eating window is one hour shorter or longer that day. The calculator tells you when that happens.
- All times are shown in your browser's time zone.
The schedules
The same templates with a daily eating window that Still offers. The first number is the hours without food, the second the eating window; OMAD (“one meal a day”) means 23 to 1.
| Schedule | Fasting | Eating window | Eating window, start 20:00 |
|---|---|---|---|
| 16:8 | 16 h | 8 h | 12:00 to 20:00 |
| 17:7 | 17 h | 7 h | 13:00 to 20:00 |
| 18:6 | 18 h | 6 h | 14:00 to 20:00 |
| 19:5 | 19 h | 5 h | 15:00 to 20:00 |
| 20:4 | 20 h | 4 h | 16:00 to 20:00 |
| 21:3 | 21 h | 3 h | 17:00 to 20:00 |
| 22:2 | 22 h | 2 h | 18:00 to 20:00 |
| OMAD | 23 h | 1 h | 19:00 to 20:00 |
5:2 is not a daily rhythm
With 5:2 you eat normally on five days a week. On the two fasting days, about a quarter of the usual energy intake is planned; the fasting days follow a fixed rhythm, for example Mondays and Thursdays (German Nutrition Society, DGE).
There is no daily eating window, so the calculator does not work out times for 5:2.
What is known
„So far, there are only a small number of clinical human studies on the effects of intermittent fasting, and their findings are not clear-cut.“
„Most concepts give no or only vague advice on food choice, so intermittent fasting alone does not usually lead to a nutritionally better diet.“
Frequently asked questions
- What does 16:8 mean?
- Fasting time is real, elapsed time: 16:8 means 16 hours without food, then the eating window opens.
- When does the eating window close?
- Your fast starts at the same clock time every day. The eating window closes when the next fast begins the following day.
- Which time zone are the times in?
- All times are shown in your browser's time zone.
- What does a 5:2 week look like?
- With 5:2 you eat normally on five days a week. On the two fasting days, about a quarter of the usual energy intake is planned; the fasting days follow a fixed rhythm, for example Mondays and Thursdays (German Nutrition Society, DGE).
- Is what I enter stored?
- Everything is calculated in your browser. Nothing you enter is sent or stored.
Keep the same rhythm, with Still
Still has these schedules as ready-made templates. Tap to start, tap to stop. The timer shows how far along your fast is.
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Sources
General information, not medical advice. The calculator works out clock times; if in doubt about whether and how to fast, talk to your doctor.