What is the optimal hours to fast daily?

November 24, 2025 •

3 min read

According to a 2022 review, participants doing intermittent fasting lost an average of 0.8–13% of their baseline body weight, highlighting its potential for weight loss. But what is the optimal hours to fast daily, and how do you choose the right schedule for your body?

Quick Summary

Explore different intermittent fasting schedules, such as 16:8, 18:6, and the Warrior Diet, to find the ideal daily fasting duration that aligns with your health objectives and daily routine.

Key Points

Start Slowly: Begin with an easier schedule, like the 12:12 or 14:10 method, to allow your body time to adapt to a new eating pattern and reduce initial side effects.
Sustainability Over Severity: The best fasting schedule is one you can adhere to consistently. The 16:8 method is a popular and flexible option for many, while longer fasts like 18:6 or 20:4 offer more intense benefits for experienced individuals.
Prioritize Nutrient-Dense Foods: What you eat during your eating window is crucial. Focus on whole foods rich in protein, healthy fats, fiber, and vegetables to feel satisfied and maximize health benefits.
Stay Hydrated: Consuming plenty of water and other zero-calorie beverages like black coffee or unsweetened tea is essential during fasting to manage hunger and prevent dehydration.
Consult a Professional: Intermittent fasting is not for everyone. Always talk to a doctor before starting, especially if you are pregnant, breastfeeding, have a history of eating disorders, or have diabetes.
Listen to Your Body: While mild hunger is normal during adjustment, persistent fatigue, dizziness, or negative symptoms indicate you may need to shorten your fasting window or adjust your approach.

Intermittent fasting (IF) is a popular approach that focuses on when you eat, rather than just what you eat. It involves cycling between periods of eating and fasting, aiming to achieve a 'metabolic switch' where the body starts burning fat for energy after glucose stores are depleted. However, there is no single answer to what is the optimal hours to fast daily. The best duration varies based on individual goals, experience, and lifestyle. This guide will explore common daily fasting schedules to help you find the right one.

Popular Daily Fasting Schedules

Various time-restricted eating (TRE) methods exist, each with a different fasting window. While generally safe for healthy adults, finding a sustainable schedule is key.

The 16:8 Method

This is a widely adopted and accessible method, particularly for beginners, involving a 16-hour fast and an 8-hour eating window. Many people skip breakfast and eat between noon and 8 p.m.. Benefits include moderate weight management, improved blood sugar control, and potential cellular repair (autophagy). Its flexibility also makes it socially convenient.

The 18:6 Method

Building on the 16:8 schedule, the 18:6 method extends the fast to 18 hours with a 6-hour eating window. This longer fast can lead to more significant fat burning, enhanced metabolic switching, increased ketone production, heightened autophagy, and higher growth hormone levels.

The 20:4 Method (The Warrior Diet)

An advanced protocol, the 20:4 method entails a 20-hour fast and a single 4-hour eating period. It is highly restrictive and suitable for experienced individuals, potentially leading to significant fat oxidation and deep autophagy.

The 12:12 Method

The most gentle daily fasting method, 12:12 involves a 12-hour fast and 12-hour eating window, often achieved by fasting overnight. It's an excellent starting point for beginners, allowing the body to adapt gradually.

Finding Your Optimal Fasting Window

Determining your ideal daily fasting hours requires experimentation and considering several factors.

Align with Your Schedule: Choose a window that fits your daily routine, including work and social commitments. Skipping breakfast or having an earlier eating window are common adjustments.
Start Gradually: Begin with shorter fasts like 12:12 or 14:10 before trying longer durations like 16:8 or 18:6 to help your body adapt and reduce side effects.
Listen to Your Body: While initial hunger is normal, discontinue or adjust your fast if you experience severe negative symptoms like dizziness or nausea.
Metabolic Response: Longer fasts promote more time in a fat-burning state. However, gradually increasing duration is crucial for smooth adjustment.

Daily Fasting Schedule Comparison Table

Here is a comparison of common daily time-restricted eating methods:


Fasting Method	Fasting Window	Eating Window	Best For	Key Benefits
12:12 Fasting	12 hours	12 hours	Beginners, circadian rhythm alignment	Easing into fasting, digestive rest
14:10 Fasting	14 hours	10 hours	Weight loss beginners, females new to IF	Gentle transition to longer fasts, improved metabolism
16:8 Fasting	16 hours	8 hours	Most people, weight management	Sustainable fat burning, insulin sensitivity
18:6 Fasting	18 hours	6 hours	Experienced fasters, enhanced fat loss	Deeper fat-burning effects, increased autophagy
20:4 Fasting	20 hours	4 hours	Advanced users, significant results	High fat oxidation, enhanced cellular repair

Maximizing Your Results: Tips for Success

To enhance the benefits of any fasting schedule:

Stay Hydrated: Drink plenty of water and calorie-free drinks like black coffee or unsweetened tea during your fast.
Focus on Nutrient-Dense Meals: Prioritize whole foods rich in protein, healthy fats, fiber, and vegetables during your eating window.
Avoid Overeating: Do not compensate for fasting by overconsuming unhealthy foods. Mindful eating is important.
Incorporate Exercise: Combine IF with physical activity, especially strength training, to maintain muscle mass and promote fat loss.
Align with Your Circadian Rhythm: Consider an earlier eating window to potentially improve results by working with your body's natural clock.

Safety First: Who Should Avoid Intermittent Fasting

IF is not suitable for everyone. Consult a healthcare provider before starting, especially if you have underlying health conditions. Avoid IF if you are pregnant, breastfeeding, under 18, have a history of eating disorders, have type 1 diabetes, or take certain medications.

Conclusion: The Most Important Hour is Consistency

Finding the optimal hours to fast daily is a personal choice. For many, the 16:8 schedule is a balanced and sustainable option. While longer fasts like 18:6 or 20:4 may offer more intense benefits for experienced individuals, consistency is key to long-term success. A sustainable schedule that supports a healthy diet is more important than the duration of the fast for realizing the benefits of improved metabolic health, weight management, and cellular function.

For additional information on intermittent fasting, visit the Johns Hopkins Medicine website.

Frequently Asked Questions

For beginners, the 12:12 or 14:10 fasting schedule is recommended, as it is the easiest to follow. You can start with a 12-hour fast overnight and gradually increase the duration as your body adapts.

Yes, intermittent fasting can help with weight loss by reducing overall calorie intake and promoting metabolic switching, where your body starts burning stored fat for energy once glucose stores are depleted.

The 16:8 method involves a 16-hour fast and an 8-hour eating window, while the 18:6 method includes a longer, 18-hour fast and a shorter, 6-hour eating window. The longer 18-hour fast can lead to more pronounced fat-burning benefits.

During your fasting period, you can drink calorie-free beverages such as water, black coffee, and unsweetened tea. Avoid any drinks with added sugar or cream, as they will break your fast.

If combined with strength training and adequate protein intake during your eating window, intermittent fasting can help preserve muscle mass while burning fat. The 16:8 method is often used by those who want to maintain muscle.

Some studies suggest that eating earlier in the day and fasting in the evening can improve insulin sensitivity and support better fat loss results by aligning with your body's natural circadian rhythm. However, the best schedule is the one you can stick with consistently.

Common side effects, especially for beginners, include hunger, fatigue, headaches, and irritability. These typically subside as your body adjusts. To minimize them, stay hydrated and start with a shorter fasting window.