Eating Window: The block of hours during which you consume all your daily calories. For 16:8, this is 8 hours; for 20:4, just 4 hours. All meals, snacks, and caloric beverages should fall within this window.
Fasting Ends At: The earliest time you can break your fast. Water, black coffee, and plain tea are generally considered acceptable during the fasting window without breaking the fast.
Next Meal Time: When your eating window opens based on the protocol. This is the same as "Fasting Ends At" for daily protocols.
Estimated Weekly Deficit: A rough estimate based on the difference between current and goal weight. This is a very simplified calculation and does not account for metabolic rate, activity level, or body composition.
How This Calculator Works
You select a fasting protocol and enter when you last ate. The tool adds the fasting hours to your last meal time to find when the fast ends, then adds the eating hours to find when the eating window closes. For OMAD, the eating window is effectively one meal. For 5:2, the schedule is weekly rather than daily. The calorie deficit estimate is a basic projection — it does not replace a detailed nutrition plan.
Quick Questions
Which protocol should I start with?
Most beginners start with 16:8, which allows an 8-hour eating window — for example, eating between noon and 8 PM. It's the least restrictive daily protocol and the easiest to maintain long-term. Consult a healthcare provider before starting any fasting regimen.
What can I consume during the fasting window?
Water, black coffee, and unsweetened tea are generally considered acceptable. Anything with calories — including cream, sugar, juice, or bone broth — will break the fast for most definitions of fasting.
Is intermittent fasting safe for everyone?
No. It is generally not recommended for people who are pregnant or breastfeeding, children and adolescents, individuals with a history of eating disorders, or people with diabetes or blood sugar regulation issues. Always consult a clinician before starting.
Does the eating window timing matter?
Some research suggests earlier eating windows (e.g., 8 AM to 4 PM) may align better with circadian rhythms and improve metabolic markers. However, adherence is the most important factor — choose a window that fits your lifestyle and social schedule.