Intermittent Fasting Calculator – Your Personalized Fasting Schedule
Calculate your intermittent fasting schedule and eating window.
Intermittent Fasting Schedules and Research
Intermittent fasting (IF) cycles between eating and fasting windows rather than restricting specific foods. The most common protocols vary fasting duration and frequency, each with different metabolic and lifestyle tradeoffs.
| Protocol | Eating Window | Fast Duration | Best For |
|---|---|---|---|
| 16:8 (Leangains) | 8 hours | 16 hours | Daily practice, most popular |
| 18:6 | 6 hours | 18 hours | Faster results, smaller eating window |
| 5:2 Diet | 5 days normal | 2 days (500 cal) | Flexibility, less daily restriction |
| OMAD (One Meal) | 1–2 hours | 22–23 hours | Advanced, significant restriction |
| Alternate Day | Every other day | 36 hours | Rapid weight loss research |
Metabolic switching to fat burning (ketosis) typically begins after 12–16 hours of fasting. A 2022 New England Journal of Medicine review found 16:8 IF produces similar weight loss to continuous calorie restriction over 12 months, with comparable effects on metabolic markers. Key tip: black coffee, tea, and water do not break a fast.
When does intermittent fasting start burning fat?
Insulin levels drop significantly after 8–12 hours without food. Fat oxidation increases substantially by hour 12–16. The transition from glucose to fat as the primary fuel source is called metabolic switching.
Can I exercise while fasting?
Yes — fasted exercise (training in the fasting window) may enhance fat oxidation. Most people adapt well to morning workouts in a 16:8 protocol. For intense training, performance may be better in the eating window initially.