16:8 intermittent fasting: how to start without overthinking it

16:8 is the most popular intermittent fasting schedule, and for good reason: it’s easy to explain and, for a lot of people, easy to fit into a normal day. It means 16 hours without eating and an 8-hour window for your meals.

If you’ve already decided to try it and just want to know how to begin, this guide is for you. We won’t promise miracle results. We’ll help you build a schedule you can actually keep.

What 16:8 actually means

The numbers are hours out of a 24-hour day:

• 16 is your fasting time. During it you typically have only water and zero-calorie drinks.
• 8 is your eating window.

The good news: a big chunk of the fast happens while you sleep. If you finish dinner at 8:00 PM and eat again at noon, you’ve done a 16:8.

Pick a window that fits your life

There’s no “correct” window. The best one is the one you can repeat. Some common options:

Eating window	Fasting	Who it often suits
12:00 PM – 8:00 PM	8:00 PM – 12:00 PM	People who aren’t hungry in the morning and have family dinners
10:00 AM – 6:00 PM	6:00 PM – 10:00 AM	People who prefer an early dinner
9:00 AM – 5:00 PM	5:00 PM – 9:00 AM	Office hours and quiet evenings

Think about your fixed commitments: dinner with family, lunch with coworkers, your workout. Build the window around them, not the other way around.

Tip: use the fasting calculator to see your window on a 24-hour clock before you start.

Your first week, step by step

Jumping straight to 16 hours can feel rough. A gentle ramp works better for many people:

1. Days 1 and 2: 12 hours. Have dinner at your usual time and breakfast 12 hours later. It’s close to what you already do.
2. Days 3 and 4: 14 hours. Push breakfast back a couple of hours. That’s a 14:10.
3. Days 5 to 7: 16 hours. If you feel fine, go for the full 16:8.

If you don’t make it one day, that’s fine. Ending at 14 hours still counts. What matters is consistency over weeks, not a perfect single day.

What to drink while fasting

During the 16 hours, most people have:

• Water, still or sparkling.
• Black coffee, no sugar or milk.
• Unsweetened tea or herbal tea.

Anything that adds calories (milk, sugar, juice, creamy drinks) generally counts as food. For more detail, read what breaks a fast.

Water is easy to forget when you’re not eating. Counting glasses helps: in Fastii you can add them with one tap while the clock runs.

What to eat in your window

16:8 tells you when to eat, not what. It isn’t a license to eat anything, and it isn’t a diet on its own. Many people feel better when their meals include protein, vegetables, fiber and enough water, and when they don’t try to “make up for” the fast by overeating.

If you have questions about your nutrition, a registered dietitian can help tailor a plan to you.

Signs to stop

Fasting isn’t for everyone or for every moment. End the fast and get advice if you feel strong dizziness, weakness, heart palpitations, or discomfort that doesn’t go away. And talk to a professional before starting if you’re pregnant or breastfeeding, have diabetes, take medication, are under 18, or have a history of disordered eating.

Keep count without thinking about it

A big part of what makes 16:8 work is not doing mental math. A clock that tells you how long you’ve gone and how long is left makes the habit nearly automatic.

That’s why we built Fastii: tap Start, the clock runs on your iPhone, your Home Screen widget and your Apple Watch, and it lets you know when you hit your goal. When you end the fast, it lands in your history and your streak goes up. No account, no ads.

The short version

• 16:8 is 16 hours of fasting and an 8-hour eating window.
• Build your window around your fixed commitments.
• Start with 12 or 14 hours and work up.
• Water, black coffee and unsweetened tea while fasting.
• Consistency matters more than one perfect day.