Free Intermittent Fasting Calculator - Eating Window

Set Up Your Schedule

Wake Time

Sleep Time

Fasting Protocol

16:8

16h fast

18:6

18h fast

20:4

20h fast

14:10

14h fast

Eating Preference

Evening Eater

Morning Eater

—

Fasting Window

16 hours

—

Eating Window

8 hours

Next Meal: —

What Is Intermittent Fasting?

Intermittent fasting (IF) is an eating pattern that cycles between periods of fasting and eating. Rather than focusing on what foods to eat, IF focuses on when to eat them. During fasting windows, you consume no calories (water, black coffee, and plain tea are allowed). During eating windows, you eat your normal meals.

IF has been shown to support weight loss, improve insulin sensitivity, reduce inflammation, and may even extend lifespan in animal studies. It is one of the simplest dietary approaches since it requires no calorie counting or food restrictions — only a consistent eating schedule.

Popular IF Protocols

16:8 (Leangains): Fast for 16 hours, eat within an 8-hour window. The most popular and sustainable protocol for beginners.
18:6: A slightly more advanced approach with an 18-hour fast and 6-hour eating window. Offers deeper fasting benefits.
20:4 (Warrior Diet): Fast for 20 hours and eat one large meal plus snacks in a 4-hour window. Intense but popular among experienced fasters.
14:10: A gentle introduction to IF with a 14-hour fast. Ideal for those new to fasting or those who prefer more flexibility.

Find the right calorie intake for your eating window using our TDEE Calculator, or plan your macros with our Macro Calculator.

Tips for Success

Start gradually — if you are new to IF, begin with a 12:12 or 14:10 protocol and work your way up.
Stay hydrated during fasting windows — drink plenty of water and herbal tea. Check your hydration needs with our Water Intake Calculator.
Break your fast gently with whole, nutritious foods rather than processed or sugary meals.
Be consistent — stick to the same eating window daily to help your body adapt.
Listen to your body — if you feel dizzy or unwell, eat something and adjust your protocol.

Frequently Asked Questions

Is intermittent fasting safe?

Intermittent fasting is generally safe for healthy adults. However, it may not be suitable for pregnant or breastfeeding women, people with eating disorders, those on diabetes medications, or individuals with certain medical conditions. Always consult a healthcare provider before starting.

What can I drink while fasting?

During fasting periods, you can drink water, black coffee, plain tea, and sparkling water. Avoid anything with calories, including sugar, milk, cream, and bone broth. Some people allow small amounts of zero-calorie sweeteners, though this may vary.

Will I lose muscle?

Short-term fasting (16-24 hours) is unlikely to cause significant muscle loss, especially if you consume adequate protein during eating windows and engage in resistance training. Longer fasts and extreme calorie restriction pose higher risk of lean mass loss.

Can I work out while fasting?

Yes, many people exercise in a fasted state. Low to moderate intensity activities like walking or yoga are well tolerated. High-intensity workouts may feel harder initially. If performance suffers, try timing intense exercise during or shortly after your eating window.

How quickly does IF work?

Results vary, but many people notice changes within 2 to 4 weeks. Initial weight loss may include water weight. Fat loss typically becomes evident after 4 to 6 weeks of consistent practice. The key is combining IF with nutritious food choices and regular activity.

Should I eat breakfast on IF?

There is no single right answer — it depends on your chosen protocol. In 16:8, many people skip breakfast and eat from noon to 8 PM. Others prefer an early eating window (e.g. 6 AM to 2 PM). Choose the schedule that best fits your lifestyle and energy patterns.

Related Calculators

Explore more health tools:

TDEE Calculator — Your total daily energy expenditure

Calorie Deficit Calculator — Set your deficit goals

Macro Calculator — Balance your macros

BMR Calculator — Find your basal metabolic rate

Keto Calculator — Ketogenic diet macros

BMI Calculator — Check your Body Mass Index