For many beginners, the best hours for intermittent fasting are not the longest hours. A 12:12 or 14:10 schedule is often a more practical starting point, while 16:8 may fit some people once the routine feels manageable. Longer fasts are not automatically better, and some longer fasts may be risky for certain people.[1][2]
Key takeaways
- Start with a fasting window you can repeat without feeling pushed into extremes.
- Many beginners do better with 12 to 14 fasting hours before trying 16 hours.
- A fast should be shortened or stopped if symptoms are persistent, severe, or feel unsafe.
- If you take medications, have diabetes, are pregnant or breastfeeding, are underweight, or have an eating disorder history, get medical guidance before fasting.
- The right fasting length should support your eating pattern, not replace nutrition quality.
Table of Contents
Common fasting lengths and who they fit
| Fasting length | Example eating window | Better fit | Be careful if |
|---|---|---|---|
| 12 hours | 7 a.m. to 7 p.m. | First-time beginners, breakfast eaters, people easing in | You still skip meals or undereat |
| 14 hours | 8 a.m. to 6 p.m. or 9 a.m. to 7 p.m. | Beginners who want structure without a big jump | It causes evening overeating |
| 16 hours | 10 a.m. to 6 p.m. or noon to 8 p.m. | People who tolerate a shorter eating window and can eat balanced meals | You rush meals, feel dizzy, or struggle with medication timing |
| 18+ hours | Often one or two meals | Experienced fasters with low-risk context | It becomes hard to hydrate, eat enough, or function well |
| 24 hours or longer | Full-day fasts | Not a default beginner choice | You have medical conditions, medications, symptoms, or no clinician guidance |
Cleveland Clinic describes 14:10 and 16:8 as common time-restricted patterns, while longer methods can be harder to tolerate.[2]
How long should an intermittent fast be for beginners?
A beginner fast should usually be long enough to create structure, but not so long that it disrupts meals, hydration, sleep, work, or social life.
A reasonable progression may look like this:
- Start with 12:12 for one to two weeks.
- Try 13 or 14 fasting hours if 12:12 feels easy.
- Consider 16:8 only if you can still eat balanced meals without rushing.
- Stay at the shortest schedule that supports consistency.
Johns Hopkins notes that adapting to intermittent fasting may take two to four weeks.[1] That means early discomfort is not always a sign to intensify the plan. Often, the better move is to keep the schedule steady or make it gentler.
How long can you do intermittent fasting as a routine?
Some adults use time-restricted eating for months or longer, but the better question is whether the routine remains healthy and sustainable. A fasting schedule should still leave room for nutrient-dense meals, enough fluids, social flexibility, and normal daily function.
Reassess the plan if you notice:
- You regularly overeat when the eating window opens.
- You skip protein or vegetables because the window is too short.
- You feel preoccupied with the clock.
- Exercise, work, or sleep becomes harder.
- You keep extending the fast to compensate for eating.
- Symptoms keep returning.
Intermittent fasting changes meal timing; it does not make total intake, food quality, or medical context irrelevant.[1]
When should you shorten or stop the fast?
Shorten or stop the fast if you have dizziness, faintness, severe headaches, confusion, persistent constipation, mood changes that feel unmanageable, binge-like eating, or symptoms that interfere with daily life.[3]
Get medical guidance before continuing if you:
- Take medications that require food or affect blood sugar.
- Have diabetes, kidney disease, heart disease, or another medical condition.
- Are pregnant, trying to become pregnant, or breastfeeding.
- Are underweight or recovering from illness or surgery.
- Have a current or past eating disorder.
A fasting window is not worth finishing when your body is giving you warning signs.
How GoFasting can help you test fasting hours
GoFasting can help you log fasting windows, weight, steps, calorie intake, and water intake, then review patterns as you adjust your routine.
If you are testing 12:12 before 14:10, tracking can show whether your chosen window is becoming easier to repeat. Keep personal observations such as hunger, sleep, mood, or digestion separate from app-tracked data unless the app explicitly supports them.
FAQ
How long should intermittent fasting last each day?
Many beginners start with 12 to 14 fasting hours. Some later try 16:8, but longer is not automatically better.
How long should I do intermittent fasting before changing the schedule?
Give a manageable schedule about two to four weeks when possible, unless symptoms, medication needs, or medical guidance indicate you should stop sooner.[1]
Is 16 hours the best intermittent fasting window?
Not for everyone. A 16-hour fast can work for some adults, but 12:12 or 14:10 may be easier and safer for beginners.
Can I do intermittent fasting every day?
Some people do, but daily fasting should still allow balanced meals and normal functioning. If it becomes rigid, stressful, or symptom-triggering, adjust the schedule.
Are 24-hour fasts better?
No. Longer fasts are not automatically better, and longer 24-, 36-, 48-, or 72-hour fasts may be dangerous for some people.[1]
How long to do intermittent fasting?
The answer depends on your fasting window, eating-window habits, health context, and whether the routine is repeatable. Use the guidance above as a starting point, and get qualified advice if medical conditions, medications, pregnancy, breastfeeding, underweight status, or eating-disorder risk apply.
How long should intermittent fasting be?
The answer depends on your fasting window, eating-window habits, health context, and whether the routine is repeatable. Use the guidance above as a starting point, and get qualified advice if medical conditions, medications, pregnancy, breastfeeding, underweight status, or eating-disorder risk apply.
Bottom line
The best fasting hours are the ones you can repeat while eating well, staying hydrated, and feeling safe. Start gently, adjust based on real-life response, and do not treat longer fasting as automatically better.
Medical disclaimer
This article is for general educational purposes only and is not medical advice. Talk with a qualified health care professional before fasting if you have a medical condition, take medications, are pregnant or breastfeeding, are underweight, have an eating disorder history, or feel unwell while fasting.
References
- Johns Hopkins Medicine. Intermittent Fasting: What Is It, And How Does It Work? https://www.hopkinsmedicine.org/health/expert-qa/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