Intermittent Fasting Window Calculator
Calculate your eating and fasting windows for 16:8, 18:6, 20:4, OMAD, and custom intermittent fasting protocols.
What this calculates
Intermittent fasting splits each day into a fasting window and an eating window. Popular ratios include 16:8 (16 hours fasting, 8 eating), 18:6, 20:4, and OMAD (one meal a day). This calculator turns a chosen ratio and your last meal time into specific start/end clock times so the schedule is concrete, not theoretical.
Formula & how it works
Fast start = end of last meal. Eating window starts at: fast_start + fasting_hours. Eating window ends after eating_hours. Repeat daily. The math is just clock arithmetic — the discipline is in actually following it.
Worked example
16:8 protocol, finished dinner at 20:00 (8 PM). Fast starts 20:00. Fasting window: 20:00 → 12:00 next day. Eating window: 12:00 → 20:00 (8 hours, e.g. lunch + dinner). For 18:6: eating window narrows to 14:00 → 20:00.
Frequently asked questions
Is intermittent fasting better than other diets?
Mixed evidence. For total calorie reduction it works as well as continuous restriction. Some metabolic benefits beyond weight loss are debated. The main appeal is structural simplicity: fewer meals to plan.
Does coffee break the fast?
Black coffee, plain tea, and water don't meaningfully impact insulin or autophagy and are generally accepted during the fast. Adding milk, sugar, or BPC turns it into food.
Should women fast?
Some research suggests women may be more sensitive to long fasts (menstrual irregularity, increased stress). Many do well on 14:10 or 16:8 but should be cautious about 20:4 or OMAD long-term.
Is OMAD safe?
Short-term, generally yes for healthy adults. Long-term concerns include nutrient deficiency (hard to eat enough variety in one meal), social difficulty, and potential disordered eating triggers. Not for everyone.
Disclaimer: Not appropriate for pregnant/nursing women, people with eating disorders, type 1 diabetes, or some medical conditions. Talk to a doctor first.
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