Intermittent Fasting Calculator

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Fasting Is About the When, Not the What

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.

Choosing a Protocol That Fits Your Life

• 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.

Making the Fast Sustainable, Not Just Startable

• 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.

Which Eating Window Suits Your Day

The calendar-compatible answer to "16:8 or 18:6?" is: what does your day actually look like? Match your natural hunger rhythm to the window instead of forcing a protocol:

• Morning eater — If you wake up hungry and your whole family eats dinner by 6 PM, an early window (e.g. 8 AM – 4 PM) makes 16:8 feel effortless. The 8-hour window lets you land two proper meals and a snack before evening social commitments begin.
• Evening eater — If you skip breakfast without thinking and dinner with friends or coworkers is a regular event, a noon–8 PM window converts 16:8 into "just skip breakfast," which is why it's the most popular variant. It keeps your appetite satisfied through late-night work or study.
• 18:6 reality check — The tighter 6-hour window usually means compressing your food into two larger meals or falling short of protein targets. It works best for people who naturally eat only twice a day; if you snack through the afternoon, 18:6 will fight your lifestyle more than your hunger.

Whichever side you fall on, this calculator lets you set wake and sleep times plus a morning or evening preference and returns a schedule synchronized to your own day — not a generic chart.

Frequently Asked Questions

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