Intermittent Fasting Calculator
Fasting Settings
Select your fasting schedule and start time to generate a localized daily fasting timeline and eating window schedule.
Fasting Schedule
Fasting & Eating Schedule
Daily schedule details computed from your start input.
Phase 1: Fasting
Phase 2: Eating Window
Medical Disclaimer
Fasting guidance is for informational purposes only and is not a substitute for medical advice. Pregnant or lactating women, adolescents in growth phases, and individuals with medical conditions like diabetes or eating disorders should consult a physician before fasting.
Intermittent-Fasting Schedule Limits
Reference date and last reviewed: July 11, 2026
Calculation Basis
Uses the entered last and first meal times and selected fasting duration to display eating and fasting windows by date.
Reference Limits
It does not determine whether fasting is appropriate for your weight, glucose, medical conditions, nutrition, or medication schedule. The timetable is not a treatment plan.
When to Confirm Officially
If you have diabetes, a history of an eating disorder, pregnancy or breastfeeding, are still growing, are underweight, have a chronic condition, or take prescription medicine, ask a health professional before fasting.
Usage Tips
Start with an intermittent fasting schedule you can keep
Jumping straight into a 20:4 or 24-hour fast can make hunger harder to manage and may lead to overeating later. If you are new to intermittent fasting, begin with a 16:8 fasting schedule and check whether the fasting end time fits your sleep, work, exercise, and meal routine. A realistic eating window is usually easier to repeat than an aggressive fasting plan.
What is Intermittent Fasting Calculator?
The Intermittent Fasting Calculator plans fasting end times and eating windows from your fasting start time and selected schedule (16:8, 18:6, 20:4, 24h, or custom). It is a schedule calculator for meal planning and records, not a live fasting timer.
How to Use
- 1Select a fasting preset (16:8, 18:6, 20:4, 24h) or choose Custom to enter your own fasting duration.
- 2Enter the time you finished your last meal or started fasting.
- 3Review the fasting phase start and end times.
- 4Review the eating window start and end times to plan meals appropriately.
- 5Copy the schedule if you want to save it in a note, food log, or calendar.
Separate the fasting end from the eating window
Last reviewed: July 11, 2026Fasting schedule formula
fasting end = start time + fasting hours; eating window = max(0, 24 − fasting hours)
The selected duration is added to the start time, and the remaining part of the 24-hour cycle becomes the eating window.
A 16:8 schedule starting at 08:00
- • Start 2026-07-11 08:00
- • 16 fasting hours
- • Current time 16:00
- 1. End = 08:00 + 16 hours = 00:00 the next day
- 2. Eating window = 24 − 16 = 8 hours; progress = 8 ÷ 16 × 100 = 50%
The fast ends at 00:00 on July 12, the eating window is 8 hours, and current fasting progress is 50%.
How to read the result
- This tool places a time window on a routine; it does not diagnose a fasting state or health outcome.
- Nutrition quality and total intake still need to be planned separately inside the eating window.
Conditions that change the result
- Duration alone cannot determine suitability for weight, glucose, nutrition, or medication needs.
- A 24-hour or longer fast can be more demanding depending on the person and context.
Common input mistakes
- Recording a midnight end time on the starting date shifts the eating window to the wrong day.
- Applying the schedule without advice during pregnancy, growth, diabetes, or an eating-disorder history can be unsafe.
Reference Knowledge
- ●The 16:8 method means fasting for 16 hours and eating within an 8-hour window. It is often the easiest starting point.
- ●18:6 and 20:4 schedules shorten the eating window, so consider your work, exercise, sleep, and social meal routines before choosing them.
- ●A 24-hour fast is more demanding and is generally better suited to experienced users or people who have discussed fasting with a professional.
- ●The eating window is the period after a fast ends when you can plan meals. Balanced meals still matter during that window.
- ●During a fast, people commonly choose water, unsweetened tea, or black coffee because they contain little to no calories.
- ●Adolescents, pregnant or lactating women, and people with diabetes, eating disorders, or other medical conditions should consult a healthcare professional before fasting.
FAQ
Q.Are zero-calorie drinks or chewing gum allowed during fasting?
Zero-calorie drinks or sugar-free gum may contain little to no energy, but some sweeteners can affect appetite or individual insulin response. For a stricter fast, plain water, black coffee, and unsweetened tea are usually the safer choices.
Q.Can I eat anything I want during the eating window?
An eating window is not a license to overeat or rely on highly processed, sugary foods. To make the schedule useful, break the fast gently and prioritize protein, fiber, and nutrient-dense whole foods.
Q.Can I edit my start time or set it to a past date?
Yes. Entering a past date and time recalculates the fasting end time and eating window from that point. This is useful when you started fasting earlier and want to organize the schedule afterward.
Q.Which fasting schedule is best for beginners?
For most beginners, 16:8 is the gentler starting point because it leaves a wider eating window. If you later try 18:6 or 20:4, adjust gradually and pay attention to fatigue, sleep, workout performance, and overeating.
Q.What should I do if I feel dizzy or get a headache during a fast?
Mild headaches or fatigue can happen early in a fast, often due to hydration and electrolyte changes. Drink water and consider electrolytes if appropriate. If symptoms worsen or you experience severe dizziness, nausea, cold sweats, or other concerning signs, stop fasting and consult a healthcare professional.
