17 Fit Intermittent fasting
Intermittent fasting a calculator for 16:8, 18:6, 20:4 and other schedules
Pick a schedule and when you last ate: you’ll see when the fast ends, when you can eat and the stages along the way, as the 17 Fit timer shows them.
Your fast
- The fast ends
- 12:00, tomorrow
- Eating window
- 12:00–20:00 (8 h)
Stages along the way
- 20:00Digesting
The body digests the last meal and absorbs nutrients. - 00:00Blood sugar settles after 4 h
Insulin levels drop and blood sugar evens out. - 04:00Glycogen stores after 8 h
The liver uses its glycogen stores to keep your energy up. - 08:00Switching to fat after 12 h
Glycogen runs low — the body uses fat as fuel more actively. - 12:00Ketosis after 16 h
Ketone levels rise — an alternative fuel for the brain and muscles.
Approximate: every body has its own pace.
Fast until 12:00, eat from 12:00 to 20:00.
A timer keeps you honest. 17 Fit starts the fast with a tap, shows the stage you’re in and keeps your history and streaks — from 12:12 to 23:1.
Schedules compared
The number before the colon is the hours of fasting, after it the hours you eat in.
| Schedule | Fast | Eating window | For whom |
|---|---|---|---|
| 12:12 | 12 h | 12 h | A gentle start: dinner to breakfast |
| 14:10 | 14 h | 10 h | A step up from 12:12 |
| 16:8 | 16 h | 8 h | The most popular: skip breakfast or a late dinner |
| 18:6 | 18 h | 6 h | Two meals in a six-hour window |
| 20:4 | 20 h | 4 h | One big meal and a snack |
| 23:1 | 23 h | 1 h | One meal a day (OMAD) |
Questions and answers
Does intermittent fasting help you lose weight?
It does when it leads to a calorie deficit: a shorter eating window often means eating less. If the window fills up with as much as before, the weight stays.
What can I drink while fasting?
In most approaches, water, black coffee and tea without sugar or milk. Anything with calories breaks the fast.
Which schedule should I start with?
12:12 or 14:10: they mostly mean no late snacks. Once that feels easy, 16:8 is the usual next step.
Who shouldn’t fast?
Pregnant and breastfeeding women, children and teenagers, people with a history of eating disorders, and anyone taking medication for diabetes or blood pressure without their doctor’s approval.
Can I exercise while fasting?
Light and moderate training usually goes fine; for hard workouts many people move them into the eating window.
Are the stages exact?
No: they are an approximate guide, and every body has its own pace. The app marks them the same way.
17 Fit
The fast in your pocket
Start it with a tap, see the stage you’re in, and keep your streak — the timer, history and stages are in the free diary.
- Timer with stages, history and streaks
- Schedules from 12:12 to 23:1
- Free food diary, no sign-up and no ads
Tools
- Calorie calculator Daily calories for weight loss, maintenance or muscle, with macros.
- Protein calculator How much protein you need a day, per meal and in real food.
- BMI calculator Body mass index and the healthy weight range for your height.
- Move your diary Bring your diary over from MyFitnessPal, FatSecret or Yazio.