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Plan{{ resultsReady ? `${computation.normalizedInputs.plan_days} days` : '—' }} Weekly fast{{ resultsReady ? formatHours(computation.values.weekly_fasting_hours) : '—' }}
This planner schedules time only; it does not assess nutrition adequacy or medical suitability.
Enter 0.25-23.75 hours.
h
Enter 0.25-23.75 hours so the pair totals one day.
h
The fast begins when the selected eating window ends.
Generate 1-30 consecutive days.
days
Day labels repeat through the selected plan length.
Children and teens, pregnancy or breastfeeding, type 1 diabetes or insulin use, eating-disorder history, and medical complexity require professional guidance.
The neutral default keeps every day on the same anchor.
{{ include_weekend_shift ? 'Enabled' : 'Disabled' }}
Use -180 to +180 minutes in 15-minute steps.
min
Leave blank when hydration cues are not needed.
Use this with wake time and a hydration interval.
Use 0 to disable, or 30-360 minutes.
min
The neutral default adds no meal-spacing guidance.
Use the cue only as a calendar placeholder.
The neutral default adds no goal-specific note.
The neutral 24-hour default does not change any preset result.
h
DayEating windowFasting windowMeal structureWorkout cueCopy
{{ row.day }}{{ row.eating_window }}{{ row.fasting_window }}{{ row.meal_structure }}{{ row.workout_cue }}

The chart renderer is unavailable. The same clock anchors remain available in the schedule table.

Planning checks
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This is an educational timing plan, not medical advice or a nutrition prescription. Stop and seek professional guidance if fasting causes concerning symptoms or conflicts with medicines, pregnancy, breastfeeding, growth, diabetes care, or eating-disorder recovery.

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Intermittent fasting changes when food is eaten by alternating defined eating and fasting periods. A daily time-restricted schedule might allow food for 8 hours and leave 16 hours without calories, while other forms use whole fasting days. A clock planner is suited to repeating daily windows, not alternate-day or multi-day fasting.

The notation puts fasting first. A 16:8 schedule means 16 fasting hours followed by an 8-hour eating window in each 24-hour cycle. Choosing a first meal fixes the rest of that cycle: if eating begins at noon, an 8-hour window ends at 20:00 and the next fast runs until noon the following day.

Timing is only one part of eating well. Food quality, total intake, hydration, sleep, exercise, medication, and individual health still matter. A narrow window can make adequate nutrition and recovery harder even when the clock arithmetic is correct, and a goal such as weight loss is not guaranteed by the schedule.

A timetable can organize A timetable cannot determine
First-meal and fast-start timesWhether fasting is medically suitable
Weekday and weekend clock shiftsEnergy, protein, vitamin, or fluid needs
Meal-spacing and reminder cuesMedication changes or glucose safety
Consistency across several daysWeight loss or health outcomes

Intermittent fasting is not appropriate for everyone. Children and teenagers, people who are pregnant or breastfeeding, people with type 1 diabetes or insulin use, anyone with an eating-disorder history, and people with medically complex needs should seek qualified guidance rather than relying on a timetable. New headaches, nausea, unusual anxiety, faintness, or other concerning symptoms deserve medical attention.

This material is informational and does not diagnose, prescribe treatment, assess nutrition adequacy, or replace advice from a clinician or registered dietitian.

How to Use This Tool:

Choose a daily cycle only after deciding that a time-based schedule is appropriate for your circumstances.

  1. Select a Fasting protocol or choose custom hours. A custom fasting/eating pair must total 24 hours within a quarter hour.
  2. Enter the First meal, plan length, and starting weekday. The first meal anchors every eating window and fast-start time.
  3. Choose the Safety context and set a Personal fasting ceiling. A protocol longer than that ceiling is rejected instead of being scheduled.
  4. Add a weekend shift only when the change is intentional. Wake and sleep times are optional as a pair; they are required if hydration reminder times are requested.
  5. Review Daily schedule and Planning checks. Change the protocol or clock anchor if a window conflicts with medication, training, sleep, or the guidance you have received.

Interpreting Results:

Read each row as a clock plan, including the “crosses midnight” note when a window continues into the next calendar day. The schedule repeats the same first-meal anchor except on Saturday and Sunday when a weekend shift is enabled.

  • Longest fasting hours adds the absolute weekend shift to the selected fast. It is a conservative transition check, not a measured fast.
  • Weekly fasting hours is seven times the daily fasting duration. It does not account for missed meals, snacks, calories in drinks, or schedule changes.
  • Hydration cues are clock reminders spaced through the entered waking window. They do not prescribe fluid volume or account for heat, exercise, illness, or medical restrictions.
  • A caution is a prompt to revise the timetable or obtain guidance. It is not evidence that a longer schedule is safe when no warning appears.

Technical Details:

Every schedule is calculated on a 1,440-minute civil clock. Times wrap at midnight, while day labels advance through the selected 1–30 day plan. Preset protocols provide fixed fasting and eating durations; custom values are rounded to the nearest quarter hour before scheduling.

Formula Core

A valid custom cycle keeps fasting and eating within one day:

|F+E−24|≤0.25

F is fasting hours and E is eating hours. Each must be from 0.25 through 23.75 hours. The quarter-hour tolerance is inclusive.

The selected first meal, expressed as minutes after midnight, anchors the fast start:

Mfast= (Mmeal+60E) mod1440

Weekly fasting hours equal 7F. When a weekend shift S is enabled, the transition estimate is F + |S|/60. Meal spacing is E divided by one fewer than the selected meal count; no spacing is calculated when fewer than two meals are selected.

Rule Core

Rule Boundary Result
Personal ceilingFasting hours > ceilingSchedule blocked
Very short eating windowFasting hours ≥ 20Extra caution added
Weekend shift−180 to +180 minutesApplied only to Saturday and Sunday
Hydration reminders0, or 30–360 minutesPositive values also require wake and sleep times
Waking windowWake and sleep both present or both blankIncomplete pair blocked

Preset pairs are 12:12, 14:10, 16:8, 18:6, 20:4, 23:1 for one meal a day, and 13:11 for the circadian option. The selected safety context changes the wording of planning checks but does not compute individual medical risk.

Limitations and Safety:

The result is a timetable only. It does not monitor an active fast, count calories, evaluate nutrients, change medicines, or predict outcomes.

  • Discuss fasting with the clinician managing diabetes, glucose-lowering medicine, pregnancy, or another relevant condition before making a schedule.
  • Do not use reminder times as a fluid prescription, particularly when illness, kidney or heart conditions, heat, or exercise changes hydration needs.
  • Stop and seek appropriate care for concerning symptoms rather than extending the fasting window to match the plan.

Worked Examples:

A later weekend first meal

A 16:8 cycle anchored at 12:00 produces a 12:00–20:00 eating window on weekdays. With a +60 minute weekend shift, Saturday and Sunday move to 13:00–21:00, and the transition estimate becomes 17 hours. That value highlights the change in rhythm; it does not declare the longer transition safe.

References: