Intermittent Fasting Schedules Explained: 12/12, 16/8, 18/6, 20/4 and OMAD
Intermittent fasting, also called time-restricted eating, means eating within a set window of the day and not eating for the rest of it. The schedules have names made of two numbers, like 16/8, which can be confusing the first time you see them.
This guide explains what each common schedule means, gives example eating windows, describes how people usually start, and covers who should be careful. It is general information, not a recommendation to fast. It ends with how to time any of these schedules in Fasting Timer.
What the two numbers mean
The first number is the hours spent fasting and the second is the hours of the eating window. The two always add up to 24, because they describe one day. So 16/8 means a 16-hour fast followed by an 8-hour window in which you eat your meals.
Sleep counts as part of the fast. That is why many schedules feel shorter than the numbers suggest: a 16-hour fast that runs from 8 pm to noon includes a full night's sleep.
This is general information, not medical or nutritional advice. Fasting is not suitable for everyone. If you are pregnant or breastfeeding, under 18, have or have had an eating disorder, have diabetes or another medical condition, or take medication, talk to a doctor before changing when you eat.
The common schedules, with example windows
12/12
A 12-hour fast and a 12-hour eating window, for example finishing dinner at 8 pm and eating breakfast at 8 am. For many people this is close to what they already do, which makes it a gentle starting point.
16/8
A 16-hour fast and an 8-hour window. A typical version is eating between noon and 8 pm, which mostly means skipping breakfast. It is probably the most widely discussed schedule. See 16/8 fasting schedule examples for windows that fit different routines.
18/6
An 18-hour fast and a 6-hour window, for example eating between 1 pm and 7 pm. This leaves room for two meals and perhaps a snack.
20/4
A 20-hour fast and a 4-hour window, for example eating between 2 pm and 6 pm. In practice this is often one main meal and a smaller one.
OMAD (one meal a day)
Eating a single meal and fasting for the rest of the day, roughly 23 hours. If you finish eating at 7 pm, the next meal would be around 6 pm the following day. It is the most restrictive of the common schedules and the hardest to get enough nutrition from.
Choosing a schedule that fits your life
The best-sounding schedule is not much use if it clashes with your work, family meals or training. Things to think about:
- When do you usually eat with other people? Put your window around those meals.
- When do you train or do physical work? Many people prefer to eat within a few hours afterwards.
- Do you work shifts? Your window can move with your sleep rather than the clock on the wall.
- Would you rather skip breakfast or a late dinner? That decides whether your window sits earlier or later in the day.
Starting gradually
People who jump straight to a long fast often find it hard to keep going. A more common approach is to start with 12/12 for a week or two, then stretch the fast by an hour at a time if it feels fine. Many stay at 14/10 or 16/8 and never go further, and that is a perfectly reasonable place to stop.
It also helps to keep the window steady from day to day rather than changing it constantly, and to eat balanced meals in the window rather than trying to make up for lost time.
Hydration and warning signs
Water is generally fine during a fast, and many people find it helps. What counts as breaking a fast (for example, black coffee or tea) is a matter of debate, so decide on a simple rule and keep to it.
Stop the fast and eat if you feel faint, dizzy, shaky, confused or unwell, and seek medical help if symptoms are severe. Feeling hungry is normal; feeling ill is not.
Timing your schedule with Fasting Timer
Fasting Timer has all five of these schedules as presets.
- On the Fasting Timer tab, choose 12/12, 16/8, 18/6, 20/4 or OMAD.
- Tap Start Fasting. The progress card shows elapsed time, remaining time, the estimated end time and the next milestone.
- Close the page if you like. The start time is saved, so the timer is still correct when you come back.
- Log drinks on the Water Intake tab with the +0.1, +0.25, +0.5 and +1.0 liter buttons.
- When you are done, tap End Fasting and choose a reason, such as Goal Achieved or Schedule Change.
- Open Fasting History to see each fast and your total count, total time, average, longest fast and a trend chart.
The web version offers only these five presets and does not send a notification when the target is reached. Fasting Timer is also available for iPhone and Android.
Frequently asked questions
What does 16/8 mean?
16 hours of fasting followed by an 8-hour eating window each day, for example eating between noon and 8 pm.
Does sleep count as fasting time?
Yes. The fast counts every hour since your last meal, including the hours you are asleep.
Which intermittent fasting schedule is best for beginners?
Many people start with 12/12 and lengthen the fast slowly. If you have any health condition, ask a doctor first.
Is OMAD the same as 23/1?
They are very similar. OMAD means one meal a day, which works out to roughly a 23-hour fast with about an hour to eat.
Can I set a custom length such as 14/10 in Fasting Timer?
Not in the web version, which has the five presets. You can start a 12/12 fast and let it run past the target, or end any fast early, and the history records the actual duration.