What's the difference between protocols?

16:8 (Leangains) — fast 16 hours, eat 8: most popular, easiest to sustain. 18:6 — slightly stricter, larger autophagy claims (evidence is mixed). 20:4 (Warrior diet) — one large meal + small snacks. OMAD (One Meal A Day) — single meal, ~1-hour eating window: hardest to sustain nutrient-densely.

Does fasting actually do anything?

Yes for weight loss (via calorie restriction and reduced snacking opportunity). Mixed evidence for metabolic-health claims (insulin sensitivity, autophagy, longevity) — most well-controlled human trials show modest effects vs equivalent calorie restriction. Don't expect magic.

Can I drink during the fast?

Standard rules: water, black coffee, plain tea — yes, any time. Anything with calories, sweeteners, or BCAAs technically breaks the fast (insulin response). Some practitioners allow 0-calorie sweeteners; it's contested.

Should women fast like men?

Mixed evidence. Some research and practitioner reports suggest women (especially of reproductive age) tolerate aggressive fasting less well than men — disrupted cycles, sleep issues, hair loss after months at 18:6+. Start gentle (14:10 or 16:8), monitor cycle and energy, back off if anything goes wrong.

Can I work out fasted?

Light cardio: yes, often improves fat oxidation. Heavy strength training: depends — performance is usually unchanged for ≤16-hour fasts but suffers at 18+. Many people time their hardest workout to break the fast (eat immediately after).

For healthy adults, generally yes. Avoid if: pregnant or breastfeeding, history of eating disorders, type 1 diabetes (without doctor supervision), under 18, very lean already, or taking medications that require food. Consult a doctor before starting.

Intermittent Fasting Window Calculator (16:8 / 18:6 / OMAD)

Health & Fitness· 18 tools

Free intermittent fasting calculator. Choose a protocol (Leangains 16:8, 18:6, 20:4 warrior, or OMAD one-meal-a-day), set when you want your first meal, and the calculator returns your eating window and the start of the fast. Useful for planning around social meals, workouts, or work schedules.

Protocol

First meal time

16:8 — Leangains, most common · Fast 16h · Eat 8h

Water, black coffee, plain tea allowed during the fast. Avoid sweeteners.

Eating window

12:00 → 20:00

8 hours

Fasting window

20:00 → 12:00

16 hours

Disclaimer: For informational purposes only. This is not medical advice — consult a qualified healthcare provider for personal recommendations.

Frequently Asked Questions

References

Effects of Intermittent Fasting on Health, Aging, and Disease — New England Journal of Medicine (2019)

Related Tools

Calorie Calculator (BMR & TDEE)
Calculate your daily calorie needs using the Mifflin-St Jeor equation for BMR and activity-adjusted TDEE.
TDEE Calculator (Total Daily Energy Expenditure)
Calculate your TDEE — the total calories you burn per day including activity. Uses Mifflin-St Jeor BMR plus an activity multiplier, with cut/maintain/bulk targets.
Macro Calculator
Split your daily calories into protein, carbs, and fat based on your goal and preferred macro ratio.

Frequently Asked Questions

References and sources

Related Tools