Intermittent Fasting Calculator

Enter your daily schedule and preferred fasting protocol. We'll calculate the optimal eating and fasting windows for your lifestyle.

Your Schedule

Wake Time

Sleep Time

Fasting Protocol

Window Preference

Your Recommended Schedule

Eating Window

12:00 – 20:00

Stop Eating By

20:00

24-Hour Timeline

00:00 06:00 12:00 18:00 00:00

Sleep Fasting Eating

Fasting Phases

00:00 06:00 12:00 18:00 00:00

Fed State (0-4h) Catabolic (4-8h) Fat Burning (8-12h) Ketosis (12-16h) Deep Ketosis (16h+)

You'll reach Fat Burning at approximately 04:00.

Fasting Hours

Eating Hours

Fasting While Asleep

Why Your Fasting Window Matters

Intermittent fasting is not just about when you eat, but about aligning your eating window with your circadian rhythm and daily schedule. A well-timed fasting window maximises the hours you spend in fat-burning and ketosis states while fitting naturally around your sleep, work and social life.

Research shows that eating earlier in the day (time-restricted eating aligned with daylight hours) may provide additional metabolic benefits. However, the best fasting schedule is the one you can stick to consistently. This calculator helps you find that sweet spot.

The fasting phases shown above reflect the metabolic transitions your body goes through during a fast: from the fed state where your body processes your last meal, through the catabolic phase where glycogen stores are tapped, into fat burning and eventually ketosis where your body primarily uses fat for fuel.

Frequently Asked Questions

How do I choose the right eating window for intermittent fasting?

The best eating window fits your daily routine. Consider when you wake up, when you feel hungriest, your work schedule, and social meal times. Most people find it easiest to skip breakfast and eat from midday to early evening.

What if I work shifts or have an irregular schedule?

Shift workers can still practise intermittent fasting successfully. The calculator adjusts to your specific wake and sleep times. The key is keeping a consistent window relative to your sleep schedule, even if that shifts day to day.

Does sleeping count as fasting time?

Yes, sleep hours count toward your fasting window. This is one of the reasons intermittent fasting is so practical — most people already fast for 7-9 hours overnight. You only need to extend that window by a few hours to reach a 16:8 protocol.

What is the best intermittent fasting protocol for beginners?

Most experts recommend starting with 14:10 or 16:8, which gives you a 10- or 8-hour eating window. These protocols are sustainable, easy to follow, and still deliver metabolic benefits. You can always tighten the window later as your body adapts.

Set this schedule in the Fasted app and track every fast

Once you find your ideal window, the Fasted app lets you lock it in with one tap. You will get reminders, automatic tracking, and a streak calendar to keep you on course.

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