Intermittent Fasting Calculator — Schedule

How does this calculator work?

Enter your fasting protocol, the time of your last meal (which starts your fasting clock), and your wake time. The calculator shows your fasting window, eating window, next meal time, and whether your eating window is currently open. The estimated caloric reduction is based on clinical research comparing time-restricted eating to ad-libitum eating patterns.

Choosing the right protocol

16:8 is the most studied and beginner-friendly protocol — most people skip breakfast and eat from noon to 8 PM. 18:6 and 20:4 are more aggressive and suitable for those with IF experience. OMAD (23:1) is the most extreme form and should only be attempted by experienced practitioners. The 5:2 protocol is calorie-restricted rather than time-restricted and works well for those who cannot commit to daily fasting windows.

Evidence-based benefits

A landmark review in the New England Journal of Medicine (de Cabo & Mattson, 2019) found that intermittent fasting triggers metabolic switching — shifting from glucose to fatty acids and ketones as fuel. This switch improves glucose regulation, increases stress resistance, and suppresses inflammation. A 2018 RCT (Sutton et al.) demonstrated improvements in insulin sensitivity and blood pressure in just 5 weeks of early 16:8 eating.

Tips for success

Stay hydrated during your fasting window — aim for 2-3 litres of water daily. Break your fast with a balanced meal including protein, healthy fats, and vegetables. Avoid high-sugar foods immediately after fasting as blood glucose sensitivity is elevated. Start with 12:12 or 14:10 if 16:8 feels too difficult, and gradually extend your fasting window over 2-4 weeks.

Methodology and caloric reduction estimates

The caloric reduction percentages displayed by this calculator are derived from published clinical trials comparing time-restricted eating (TRE) with ad-libitum eating. A meta-analysis by Varady et al. (Nat Rev Endocrinol, 2022) reported that 16:8 TRE reduces daily caloric intake by approximately 10-20% without conscious calorie counting. More restrictive windows (18:6, 20:4, OMAD) show progressively larger reductions of 15-30%, while the 5:2 protocol achieves roughly 25% weekly caloric reduction. These estimates are population averages and individual results vary based on meal composition, adherence, and baseline intake. The metabolic switching mechanism described by de Cabo and Mattson (NEJM, 2019) underpins the health benefits beyond simple caloric restriction.