Intermittent Fasting Calculator
Plan your intermittent fasting schedule and daily calories. Pick a protocol (16:8, 18:6, 20:4, OMAD) to get your eating window and calorie target.
11:00 AM – 7:00 PM
8-hour window, 16-hour fast
1891
kcal/day
3
meals
630
kcal/meal
Note: Intermittent fasting controls when you eat, not how much — the calorie target still determines weight change. The window starts a few hours after waking; shift it to fit your schedule.
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Calculation Method
Intermittent fasting (IF) restricts when you eat rather than what you eat, alternating a daily eating window with a longer fast. This calculator builds your eating-window schedule from your wake time and chosen protocol, and pairs it with a daily calorie target estimated from your TDEE (Mifflin-St Jeor) so the plan still matches your goal.
How the Schedule Works
Window end = start + eating-window length
Fast length = 24 − eating-window length
Calories/meal = daily target / meals in window
The protocol name shows the fast-to-feed ratio. In 16:8, you fast 16 hours and eat within an 8-hour window; OMAD means one meal a day.
Common Protocols
| Protocol | Fast | Window | Typical meals |
|---|---|---|---|
| 16:8 | 16 h | 8 h | 3 |
| 18:6 | 18 h | 6 h | 2 |
| 20:4 | 20 h | 4 h | 2 |
| OMAD | 23 h | 1 h | 1 |
Worked Example
Waking at 7:00 AM on 16:8 with a 2,000 kcal target:
- Window start = 7:00 + 4 h = 11:00 AM
- Window end = 11:00 + 8 h = 7:00 PM
- Three meals of about 667 kcal each within the window
Why It Can Help
A shorter window naturally limits snacking and often reduces total intake, which is the real driver of weight change. During the fast, stick to water, black coffee, or tea. Shift the window earlier or later to fit work, training, and sleep.
Note: This is an educational tool, not medical advice. Fasting is not appropriate for everyone — including those who are pregnant, have a history of disordered eating, or take certain medications. Consult a healthcare professional before starting.
Frequently Asked Questions
16:8 means fasting for 16 hours and eating within an 8-hour window each day - for example, eating from noon to 8pm. It is the most popular and beginner-friendly fasting protocol.
It helps mainly by making it easier to eat fewer calories within a shorter window. Fasting itself does not bypass calorie balance, so your daily calorie target still determines fat loss.
Yes, many people train fasted without issue. For hard or long sessions, performance may dip; timing some carbs and protein near training or breaking the fast around workouts can help.
What is 16:8 intermittent fasting?
Does intermittent fasting help weight loss?
Can I work out while fasting?
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