Intermittent fasting schedules explained
The common patterns, what the numbers mean, example clock times and what research does and does not show.
Talk with a healthcare professional before changing how you eat if you have a medical condition, take medication, are pregnant or breastfeeding, are under 18, or have a history of disordered eating. Stop and seek help if you feel unwell.
What the numbers mean
Daily schedules are written as two numbers that add up to 24: hours without food first, then hours in the eating window. 16:8 means 16 hours outside the window and an 8-hour eating window. Weekly patterns such as 5:2 work differently and describe days of the week.
Daily time-restricted patterns
| Pattern | Eating window | Example window | Notes |
|---|---|---|---|
| 12:12 | 12 hours | 07:00–19:00 | Close to many people’s normal overnight gap |
| 14:10 | 10 hours | 09:00–19:00 | Often a next step from 12:12 |
| 16:8 | 8 hours | 12:00–20:00 | The most widely described pattern |
| 18:6 | 6 hours | 12:00–18:00 | A short window that leaves less time for meals |
Johns Hopkins Medicine describes the 16:8 approach as eating during an eight-hour window and fasting for 16 hours. Use the eating-window calculator to try your own times.
Weekly patterns
- 5:2. Usual eating on five days a week and much-reduced intake on two non-consecutive days. Johns Hopkins describes the reduced days as a single meal of about 500–600 calories.
- Alternate-day fasting. Days of usual eating alternate with days of little or no food. The National Institute on Aging lists it among the patterns studied.
- Periodic fasting. Intake is restricted for several consecutive days, for example five days once a month. This is a research and medically supervised approach rather than something to try alone.
The tools on this site are designed for daily time-based patterns of up to 24 hours. They do not plan calorie intake.
What research shows
Interest in fasting has grown faster than the evidence. The National Institute on Aging’s overview notes that most human studies have been small, short and focused on weight, that results do not always carry over from animals to people, and that there is not yet enough evidence to recommend any fasting regimen to the public. An NIDDK interview with a fasting researcher describes intermittent fasting as a promising but still early option for type 2 diabetes, and stresses that people taking insulin or sulfonylureas must work closely with their doctors to adjust medicines. Longer-term effects are still being studied.
What to expect at first
Johns Hopkins notes that it can take two to four weeks to get used to a new routine and that people may feel hungry or irritable at first. It advises talking to a doctor if you experience unusual anxiety, headaches, nausea or other symptoms. Our guide Is intermittent fasting right for you? covers who should get advice first.
Choosing a pattern
The best pattern is one that fits your health, sleep, work and family life. Many people start with 12:12 and only lengthen the window gap if it suits them. A pattern you can keep comfortably, with enough food and sleep, matters more than the size of the first number.
Reviewed October 2026 by Lee Palmer · How we write our guides · Report an error