How Intermittent Fasting Schedules Work
Intermittent fasting (IF) cycles between periods of eating and fasting on a set schedule. The two numbers in a protocol name (like 16:8) refer to fasting hours : eating hours. This calculator converts your chosen protocol and preferred start time into exact clock times for your eating window and fasting period.
Eating Window Hours = 24 − Fasting Hours
Eating Window End = Start Time + Eating Window Hours
Eating Window End = Start Time + Eating Window Hours
Common Intermittent Fasting Protocols
| Protocol | Fasting Hours | Eating Window | Difficulty |
|---|---|---|---|
| 14:10 | 14 | 10 hours | Beginner-friendly |
| 16:8 | 16 | 8 hours | Most popular / moderate |
| 18:6 | 18 | 6 hours | Intermediate |
| 20:4 | 20 | 4 hours | Advanced (Warrior Diet) |
| 23:1 | 23 | 1 hour | Advanced (OMAD) |
Tips for Success
- Water, black coffee, and plain tea generally don't break a fast and can help manage hunger.
- Start with a shorter protocol (14:10 or 16:8) and extend gradually as your body adapts.
- Time your eating window around your schedule — many people prefer to skip breakfast rather than dinner.
❓ Frequently Asked Questions
Does intermittent fasting mean I can eat anything during my window?
Technically yes, but most health benefits associated with IF come from also eating a balanced, reasonably portioned diet during the eating window — fasting alone doesn't offset consistently poor food choices.
What can I drink during the fasting period?
Water, black coffee, and plain tea (without sugar, milk, or cream) are generally considered acceptable during a fast since they contain negligible calories and don't significantly affect insulin levels for most people.
Which protocol should a beginner start with?
14:10 or 16:8 are the most commonly recommended starting points, as they're easier to sustain while your body adjusts to the new eating pattern.
Is intermittent fasting safe for everyone?
No — IF isn't recommended for pregnant or breastfeeding women, people with a history of eating disorders, those with certain medical conditions like diabetes on specific medications, or children. Consult a doctor before starting, especially with any health concerns.
Can I change my eating window start time day to day?
Yes, many people adjust their window slightly for social occasions or schedule changes — consistency helps some people adapt faster, but the schedule can be flexible based on your lifestyle.
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📅 Last Updated: September 2026.