Many beginners do better starting with 12 to 14 fasting hours before trying 16 hours. A 16-hour fast, often called 16:8, is common, but it is not the right starting point for everyone. Longer fasts are not automatically better, and some longer fasts may be dangerous for some people.[1]
The right intermittent fasting hours depend on your current routine, eating window, symptoms, medications, medical history, and whether the schedule is repeatable. If you are unsure, start gently and adjust before extending the fast.[2]
Key takeaways
- 12:12 or 14:10 is often a more practical starting point than a longer fast.[2]
- 16:8 can fit some people after they adapt, but it is not required for intermittent fasting.
- 24-hour or longer fasts are harder and should not be treated as a better default.[1][2]
- Water, black coffee, and unsweetened tea are simple fasting-window drinks.[3]
- Medical conditions, medications, pregnancy, breastfeeding, underweight status, or eating-disorder risk change the decision.[4]
Table of Contents
A quick answer by experience level
If you are new to intermittent fasting, begin with a schedule that mostly uses the overnight period. This reduces the need to skip multiple meals and makes it easier to notice how your body responds.
| Experience level | Fasting hours to consider | Why it may fit |
|---|---|---|
| New beginner | 12 hours | Builds a clear no-snacking overnight boundary |
| Comfortable beginner | 14 hours | Adds structure without a very short eating window |
| Adapted beginner or intermediate | 16 hours | Common daily time-restricted eating pattern |
| Advanced or clinician-guided | 24 hours or more | Harder to tolerate and not a default beginner step |
For help choosing a schedule, read How to choose your plan?.
Common intermittent fasting hours
Intermittent fasting hours describe how long you fast and how long you eat. The clock times can vary, but the fasting-to-eating pattern is the main structure.
12:12 fasting
A 12-hour fast and 12-hour eating window might look like 7 p.m. to 7 a.m. fasting. This is often the easiest place to start because it mainly removes late-night eating.
It may fit if you:
- Are new to fasting
- Want a low-pressure start
- Eat breakfast and dinner with family or work routines
- Need a schedule that feels close to normal eating
14:10 fasting
A 14-hour fast and 10-hour eating window might look like 7 p.m. to 9 a.m. fasting. It can be a bridge between 12:12 and 16:8.
It may fit if you:
- Already tolerate overnight fasting
- Want a bit more structure
- Prefer not to skip a full meal
- Notice that 16:8 feels too restrictive
16:8 fasting
A 16-hour fast and 8-hour eating window might look like 8 p.m. to 12 p.m. fasting. It is common, but common does not mean required.
It may fit if you:
- Have already adjusted to 12:12 or 14:10
- Can eat balanced meals in an 8-hour window
- Do not overeat when the window opens
- Do not have medical or medication concerns that make skipped meals risky
For a full article on this schedule, see 16/8 Intermittent Fasting Guide.
24-hour or longer fasts
Some intermittent fasting patterns include 24-hour fasting periods. These can be harder and may cause more symptoms.[2] Johns Hopkins Medicine notes that longer fasts, including 24-, 36-, 48-, and 72-hour fasts, are not necessarily better and may be dangerous for some people.[1]
Do not use long fasts as a shortcut if a shorter daily routine is not working.
Who may fit shorter or longer fasting windows
Choose fasting hours based on fit, not pressure.
| Situation | More reasonable direction |
|---|---|
| New to fasting | Start with 12:12 or 14:10 |
| Late-night snacking is the main issue | Try a 12-hour overnight fast first |
| 16:8 causes overeating | Return to 14:10 or widen the eating window |
| You need breakfast with medication | Do not skip it without medical guidance |
| Symptoms are persistent or severe | Stop or shorten the fast and get guidance |
| You want faster weight loss | Adjust meals and drinks before extending fasting hours |
The fasting length should make your routine clearer, not more chaotic.
How to start without jumping too far
A gradual start is usually more useful than a perfect schedule on paper.
- Pick your current natural overnight fast. If you already stop eating at 8 p.m. and eat at 7 a.m., you are near 11 hours.
- Add 30 to 60 minutes for one week. Close the eating window a little earlier or open it a little later.
- Keep meals balanced. Do not make the eating window so short that you skip protein, fiber, or fluids.
- Keep fasting drinks simple. Water, black coffee, and unsweetened tea are common options.[3]
- Review the pattern. If you feel worse, overeat, or cannot repeat it, shorten the fast.
GoFasting can help you log fasting windows and review patterns as you adjust your routine. Tracking can show whether you are repeating the plan, but it does not decide whether a fasting schedule is medically appropriate.
Do fasting times have to be fixed every day?
Fasting times do not have to be identical every day for most general routines. Many people find it easier to keep the fasting length similar while letting the exact clock times shift with work, family, or social plans.
For example:
- Weekday: 8 p.m. to 10 a.m. fasting
- Weekend: 9 p.m. to 11 a.m. fasting
That is still a 14-hour fast. The main issue is whether the routine remains consistent enough to support your goal without becoming stressful.
For more detail, read Do fasting times have to be fixed every day.
When fasting hours should not be self-guided
Do not choose fasting hours on your own if medications, diabetes, kidney disease, pregnancy, breastfeeding, underweight status, recovery from illness or surgery, or eating-disorder risk are part of the picture.[4]
Side effects can include tiredness, dizziness, headaches, mood changes, constipation, diabetes management issues, and menstrual effects.[5] If symptoms are persistent, severe, or feel unsafe, stop or shorten the fast and get medical guidance.
If you are comparing fasting windows, these connected questions can help you choose and adjust the schedule: What other drinks can you drink?.
FAQ
How long is an intermittent fast?
An intermittent fast can be 12, 14, 16, or more hours depending on the method. Many beginners start with 12:12 or 14:10 before trying 16:8.[1][2]
How long should you intermittent fast?
Start with the shortest fasting window that gives you structure and still feels repeatable. For many beginners, 12 to 14 hours is more reasonable than starting at 16 hours.
How long should I fast for intermittent fasting if I want weight loss?
Do not choose fasting hours based only on weight loss. The eating window, total intake, drinks, activity, sleep, stress, and medical context all matter. If the schedule leads to overeating, a shorter fast may work better than a longer one.[6]
How long does it take intermittent fasting to work?
Adaptation can take a few weeks for some people.[1] For weight or habit changes, look at patterns over several weeks rather than judging from a few days.
What can I drink during fasting hours?
Water, black coffee, and unsweetened tea are simple fasting-window choices.[3] Sweetened drinks, juice, alcohol, milk, cream, and calorie-containing add-ins belong in the eating window.
Bottom line
Intermittent fasting hours should fit your life and safety needs. Start with 12 to 14 hours if you are new, consider 16 hours only when shorter fasts feel manageable, and do not treat longer fasts as automatically better. The right schedule is the one you can repeat while eating enough balanced meals and respecting medical boundaries.
Medical disclaimer
This article is for general educational purposes only and is not medical advice. Speak with a qualified health professional before starting or changing a fasting routine if you have a medical condition, take medications, are pregnant or breastfeeding, are underweight, have a history of an eating disorder, or experience symptoms that concern you.
References
- Johns Hopkins Medicine. Intermittent Fasting: What Is It, And How Does It Work?
- Cleveland Clinic. Intermittent Fasting: What It Is, Benefits and Schedules
- Johns Hopkins Medicine. Intermittent Fasting: What Is It, And How Does It Work?
- Cleveland Clinic. 6 Tips for Fasting Safely
- Mayo Clinic. Intermittent fasting: What are the benefits?
- Harvard Health Publishing. Should you try intermittent fasting for weight loss?