There is no single required fasting length for everyone. If you are new to intermittent fasting, a 12- to 14-hour overnight fast is a reasonable place to start.[2][3][4] If that feels comfortable and you can still eat balanced meals, 16:8 may be a possible next step. Longer fasts are not automatically better, and fasts of 24 hours or more can be harder to tolerate or unsafe for some people.[2][3]
The right fasting length is the shortest window that supports your goal without causing persistent symptoms, inadequate nutrition, medication problems, or an unhealthy relationship with food. Fasting is optional; it is a way to structure eating, not a requirement for health.
Key takeaways
- 12:12 and 14:10 are gentler starting points for many beginners.
- 16:8 is common, but it is not the only valid intermittent-fasting schedule.
- 18:6, 20:4, 24-hour, and multi-day fasts are more restrictive and should not be treated as default beginner options.
- Longer fasting does not guarantee greater weight loss or better health outcomes; overall intake, food quality, activity, sleep, and consistency still matter [1][2].
- If a window causes dizziness, weakness, poor sleep, binge-like eating, or difficulty meeting nutrition needs, shorten it or stop.
- Diabetes, medication use, pregnancy, breastfeeding, low body weight, chronic illness, and eating-disorder history require professional guidance.
Table of Contents
- Key takeaways
- What does intermittent-fasting length mean?
- How common fasting lengths compare
- How long should a beginner fast?
- How long should you try a schedule?
- Is 16:8 the correct amount of fasting?
- Does fasting longer lead to more weight loss?
- How often should you fast?
- What can you have during the fasting window?
- How to tell whether the fasting length is working
- When should you keep the fast short or avoid fasting?
- FAQ
- Bottom line
- Medical disclaimer
- References
What does intermittent-fasting length mean?
Daily time-restricted eating schedules are usually written as fasting hours followed by eating hours:
- 12:12 means 12 hours fasting and a 12-hour eating window.
- 14:10 means 14 hours fasting and a 10-hour eating window.
- 16:8 means 16 hours fasting and an 8-hour eating window.
- 18:6 means 18 hours fasting and a 6-hour eating window.
The clock times can vary. For example, 8 p.m. to 8 a.m. is a 12-hour fast, while 8 p.m. to noon is a 16-hour fast. The method describes the length of the fasting and eating periods, not a mandatory breakfast or dinner time.
Other methods use a weekly pattern, such as 5:2, or include a full 24-hour fast. These are different from daily time-restricted eating and should not be presented as interchangeable beginner plans.
For a detailed comparison of eating windows, see intermittent fasting eating windows: 8, 16, and 18 hours.
How common fasting lengths compare
| Schedule | Fasting / eating period | Possible fit | Main watch-out |
|---|---|---|---|
| 12:12 | 12 hours / 12 hours | Beginners or people reducing late-night snacking | May feel like a small change, but it can still create useful structure |
| 14:10 | 14 hours / 10 hours | People comfortable with an overnight fast | Do not let the shorter eating window reduce meal quality or total intake |
| 16:8 | 16 hours / 8 hours | People who already tolerate shorter eating opportunities | Meals may feel rushed or too large if the window is too tight |
| 18:6 | 18 hours / 6 hours | Some experienced fasters who remain well nourished | Harder to fit adequate protein, fiber, fluids, and calories |
| 24 hours or more | A full day or longer without food | Not a default beginner approach | Greater difficulty and more potential for symptoms or medical complications |
| 5:2 | Five usual-intake days and two lower-intake days | A weekly rather than daily structure | Restricted days still require careful nutrition and may not suit everyone |
This is a comparison, not a recommendation to progress through every schedule. A shorter window you can repeat calmly may be more useful than a longer fast that causes problems or is abandoned.[2][3]
How long should a beginner fast?
Start with your natural overnight gap. If you finish dinner at 8 p.m. and eat breakfast at 8 a.m., you are already close to 12 hours. Keep that pattern for several days and review hunger, energy, sleep, digestion, mood, and whether you can eat balanced meals.
If 12:12 feels stable, you may test 14:10 by moving the first meal slightly later or finishing the last meal slightly earlier. Only consider 16:8 if you can still eat enough and the schedule does not cause persistent discomfort or rebound eating.
A simple progression is:
- Start with 12:12 if fasting is new.
- Try 14:10 if the overnight fast feels comfortable.
- Consider 16:8 only when the shorter eating window remains practical.
- Treat 18:6 and 24-hour fasting as optional, more restrictive approaches—not required milestones.
You do not have to progress. Staying at 12:12 or 14:10 is a valid outcome if it fits your life better.
How long should you try a schedule?
Give a manageable schedule enough time to evaluate, but do not wait through warning signs. One to two weeks can reveal whether you can complete the window, eat normally, sleep well, and maintain hydration. Some people need longer to adapt, while others find a particular window is not a good fit.
Review:
- Can you complete the fast without feeling unwell?
- Can you eat enough protein, fiber, and overall food in the eating window?
- Are meals calm and moderate rather than rushed or oversized?
- Is sleep stable?
- Is the schedule compatible with work, family, social plans, and exercise?
- Does it reduce unplanned eating, or does it create a restrict-then-overeat cycle?
If the answers are mostly positive, repeat the same window before making it harder. If the answers are negative, shorten the fast. For help choosing a window around your lifestyle, see how to choose an intermittent fasting schedule.
Is 16:8 the correct amount of fasting?
No. 16:8 is popular because it is easy to describe, but popularity does not make it medically required or universally effective. The page 16:8 intermittent fasting covers that specific method in more detail.
Choose 16:8 only when it leaves enough time for balanced meals, hydration, medication requirements, social life, and recovery from activity. If you regularly skip needed meals, feel weak, sleep poorly, or overeat when the window opens, 14:10 or 12:12 may be a better fit.
Does fasting longer lead to more weight loss?
Not reliably. Fasting can help some people reduce eating opportunities, but weight change depends on longer-term energy intake, food quality, activity, sleep, stress, and adherence. A longer fast can backfire if it leads to large meals, low-quality food choices, or repeated compensation.
Current evidence does not establish that intermittent fasting is consistently superior to traditional dietary advice for weight loss. A Cochrane review found intermittent fasting may make little to no difference to weight loss and quality of life compared with traditional dietary advice in adults with overweight or obesity, although the available studies were mostly short term [1].
Use fasting hours as a structure that may help you eat in a way you can sustain, not as a guarantee of faster results.
How often should you fast?
The frequency depends on the method and your ability to repeat it without harm. Daily time-restricted eating may use a similar window most days, while other plans use selected days each week. You do not need to “make up” for a shortened fast by extending the next one.
It is reasonable for exact clock times to shift with work, travel, family meals, or weekends if the pattern remains comfortable. Consistency does not require rigid perfection.
Frequency by pattern
| Pattern | How often it is usually organized | What to check |
|---|---|---|
| 12:12, 14:10, or 16:8 | A similar window on most days | Whether daily meals, sleep, activity, and medication timing remain workable |
| A flexible time-restricted routine | The window shifts with work or social plans | Whether flexibility still prevents late-night grazing without creating compensation |
| 5:2 or selected-day restriction | Two planned days within a week, with usual eating on other days | Whether restricted days cause overeating, symptoms, or inadequate nutrition |
| 24-hour or longer fasting | Occasional and more demanding, not a required weekly milestone | Health context, prior intake, medication, hydration, and professional guidance |
Missing one day does not require a longer fast afterward. The useful measure is whether the pattern remains safe and repeatable over time, not whether every day follows the same clock.
What can you have during the fasting window?
For a clean fast, many people choose plain water, black coffee, or unsweetened tea. Calorie-containing drinks, milk, cream, juice, alcohol, protein shakes, and food belong in the eating window. See what you can drink during intermittent fasting for detailed beverage guidance.
During the eating window, build meals around protein, vegetables or fruit, fiber-rich carbohydrates, healthy fats, and enough total food. Fasting should not make it difficult to meet basic nutrition needs.
How to tell whether the fasting length is working
Review the schedule after one or two weeks, then continue checking it periodically. A suitable window should be compatible with:
- normal meals rather than rushed or oversized meals;
- stable energy, concentration, mood, and sleep;
- exercise and recovery when those are part of your routine;
- hydration and bowel habits;
- social and family meals;
- a calm relationship with food.
If the only way to complete the fast is to ignore symptoms, skip medication-related food, or compensate with overeating, the window is too restrictive for that situation. A shorter window is a valid endpoint, not a step backward.
When should you keep the fast short or avoid fasting?
Do not select fasting hours as a self-guided experiment if you:[3][4]
- have diabetes or use insulin or glucose-lowering medication;
- take medication that requires food or affects hydration or blood pressure;
- are pregnant or breastfeeding;
- are under 18, underweight, or recovering from illness or surgery;
- have kidney, liver, heart, or gastrointestinal disease;
- have a current or past eating disorder or fasting triggers rigid food rules;
- are an older adult with concerns about muscle loss or inadequate intake.
Stop or shorten the fast for fainting, severe or repeated dizziness, confusion, marked weakness, persistent vomiting, dehydration symptoms, or any symptom that feels unsafe. The fasting warning signs and when to stop guide provides additional safety context.
FAQ
How many hours should I fast each day?
There is no universal number. Many beginners start with 12 to 14 hours, then consider 16:8 only if the shorter window feels comfortable and still allows balanced meals. Longer is not automatically better.
How long is an intermittent fast?
Common daily schedules include 12:12, 14:10, 16:8, and 18:6. Some approaches use 24-hour fasts or a weekly 5:2 pattern. The appropriate choice depends on your health, routine, and ability to meet nutrition needs.
Is 12 hours of fasting enough?
It can be. A 12-hour overnight gap may provide useful structure, especially by reducing late-night eating. You do not need to extend it if a longer window makes your routine harder.
Is 14:10 better than 16:8?
Neither is universally better. 14:10 provides a longer eating window, while 16:8 is more restrictive. Choose the one that supports adequate food, sleep, energy, and consistency.
Is 18:6 safe for beginners?
It is a more restrictive option and is not necessary as a beginner starting point. If it makes it difficult to eat enough, causes symptoms, or encourages overeating, use a shorter fast.
Is a 24-hour fast necessary for weight loss?
No. A 24-hour fast is not required for weight loss and is more demanding. Results depend on overall intake and sustainable habits, not simply the longest fasting period.
Do I have to fast every day?
No. Daily time-restricted eating is one option, but other patterns use selected days. Do not compensate for a missed or shortened fast with an extreme fast the next day.
How long does it take to see results?
Adaptation, habit changes, and weight changes occur on different timelines. Review the routine over several weeks, and do not judge its success from one day or one weigh-in.
Bottom line
Start with the shortest fasting window that fits your life and leaves room for balanced meals. For many beginners, that means 12:12 or 14:10. 16:8 is an optional next step, not a requirement, and 24-hour or longer fasts should not be treated as a default. If the schedule causes symptoms or makes adequate nutrition difficult, shorten it or stop and seek guidance.
Medical disclaimer
This article is for general education only and is not medical advice. Speak with a qualified healthcare professional before starting or changing fasting if you have a medical condition, take medication, are pregnant or breastfeeding, are underweight, have a history of an eating disorder, or experience concerning symptoms.
References
- Cochrane. Intermittent fasting, traditional dietary advice or no treatment: which works better to help adults living with overweight or obesity lose weight? https://www.cochrane.org/evidence/CD015610_intermittent-fasting-traditional-dietary-advice-or-no-treatment-which-works-better-help-adults
- Johns Hopkins Medicine. Intermittent Fasting: What Is It, And How Does It Work? https://www.hopkinsmedicine.org/health/wellness-and-prevention/intermittent-fasting-what-is-it-and-how-does-it-work
- Cleveland Clinic. Intermittent Fasting: What It Is, Benefits and Schedules https://health.clevelandclinic.org/intermittent-fasting-4-different-types-explained
- Mayo Clinic. Intermittent fasting: What are the benefits? https://www.mayoclinic.org/healthy-lifestyle/nutrition-and-healthy-eating/expert-answers/intermittent-fasting/faq-20441303