Intermittent Fasting Schedule Calculator

What is intermittent fasting?

Intermittent fasting (IF) is the practice of restricting all calorie intake to a defined window each day, ranging from 10 hours (14:10) to a single meal a day (OMAD). The biological rationale combines a controlled calorie deficit, lower 24-hour insulin exposure and a longer overnight period in which the body relies on fat oxidation. Randomised trials show that IF produces fat loss similar to traditional calorie restriction when calories are matched, but participants often find adherence easier because there are fewer meals to manage. IF is not magic: people who add an evening meal beyond their daily calorie need will gain weight despite the fasting window. It is also not appropriate for everyone — pregnant or breastfeeding women, children, anyone with a history of disordered eating and several clinical conditions should not adopt restrictive fasting without medical supervision.

How to use the schedule

Pick a protocol — 14:10 is the gentlest entry. 16:8 is the modern default. 18:6 and 20:4 increase the daily fast. OMAD packs all calories into a single meal — start there only after weeks of practice.
Set the last-meal time — Type or scroll the time you finished dinner. The calculator runs a rolling 24-hour clock from that moment.
Read the eating window — The cards show when the fast ends, when the eating window closes, and the size of the window. Plan two or three balanced meals inside the window.
Hydrate during the fast — Water, plain coffee, plain tea and electrolytes do not break a fast. Anything with calories does. Aim for 30–35 ml of water per kg of bodyweight on fasting days.

How the schedule is built

Protocols are written as fast:eat hours that sum to 24. The calculator adds the fasting hours to the last-meal timestamp to produce the fast-end time, then adds the eating hours to find the close of the window. Times wrap around midnight automatically.

Common protocols

Pick the protocol that fits your social calendar and energy needs. The right schedule is the one you can keep without obsessing.

Protocol	Fast	Window	Best for
14:10	14h	10h	Beginners and people with morning training.
16:8	16h	8h	Standard for most adults; matches a no-breakfast lifestyle.
18:6	18h	6h	Experienced fasters chasing more autophagy time.
20:4	20h	4h	"Warrior" diet — one large evening meal plus light snacks.
OMAD	23h	1h	Advanced; only after months of comfortable 16:8 or 20:4.

Frequently asked questions

Will fasting break my metabolism?

Short fasts (under 24 hours) do not lower resting metabolic rate. Repeated very-low-calorie days will, but that is a calorie problem, not a fasting problem.

Can I drink coffee in the fast?

Black coffee, tea and water do not break the fast. Add milk, cream or sugar and you do — even a splash of oat milk has calories.

Is OMAD safe long-term?

Some people thrive on it; others develop nutrient deficiencies because it is hard to fit micronutrients into one plate. If OMAD becomes obsessive or causes binge episodes, stop and revert to a wider window.

Can women fast like men?

Many women do, but a sub-group reports menstrual disturbances on long protocols. If your cycle changes, shorten the fast to 12–14 hours and reassess.

Will I lose muscle?

Not if you keep protein at 1.6–2.2 g/kg, train with weights and avoid an aggressive deficit. Studies on 16:8 plus resistance training show muscle preservation comparable to standard diets.

Is this medical advice?

No. Intermittent fasting is contraindicated in pregnancy, breastfeeding, type 1 diabetes, eating disorder history and several other conditions. Talk to your doctor before changing a clinical regimen.

Intermittent Fasting Schedule Calculator