What is intermittent fasting?

What intermittent fasting is

In everyday language, intermittent fasting means repeating cycles of fasting and eating. Fasting here usually means no caloric food or drink for a chosen stretch. Water is almost always allowed. Many people also drink black coffee or unsweetened tea. A drink with meaningful calories usually ends a strict fast. What counts as ending a fast is in our article What usually ends a fast.

Diets that focus only on what you eat (calories, macros, food groups) are a different lever. Intermittent fasting focuses mainly on when you eat. You can combine it with any eating style, or simply keep a gentler daily window without calling it a lifestyle brand.

Everyday versions include skipping late-night snacks, delaying breakfast, or finishing dinner earlier so the overnight gap stretches into the morning. Named plans are optional. The pattern is a deliberate gap between meals.

Common schedules (and what the numbers mean)

Schedules are often written as fasting hours : eating hours. 16:8 means about 16 hours without calories and 8 hours when you eat, for example noon to 8 p.m. 18:6 is a shorter eating window. 14:10 and 12:12 are gentler starting points. One meal a day (OMAD) compresses eating into roughly one sitting. That is a hard first try for many people.

Alternate-day fasting and multi-day stretches are different. A daily window is not the same as a 48-hour or 72-hour fast, even though both involve not eating for a while. Read Common fasting schedules for more information.

No single ratio is best for everyone. The useful schedule is one you can keep without ignoring sleep, stress, medicines, training, or health, and one you can stop or shorten when life requires it.

What intermittent fasting is not

It is not a magic cure or a guaranteed way to lose weight, and it does not replace medical care. Results and side effects vary widely. Eating hours still need real meals: energy, protein, and ordinary food still matter.

Longer is not automatically better. Dizziness, confusion, fainting, severe weakness, or panic is a reason to stop, not a sign of discipline. See When to stop a fast.

Names such as Ketosis or Autophagy Window on this timer follow elapsed hours. They are stage names, not lab results. Read What the stages on the timer mean for more information.

Who should read the safety note first

Fasting is not appropriate for everyone. People who are pregnant or breastfeeding, under 18, underweight, or recovering from disordered eating often should not fast unsupervised. Diabetes, kidney disease, and medicines that affect blood sugar or blood pressure also change the picture.

If any of that might apply to you, or you are unsure, read Who should be careful with fasting and talk with a clinician before you start or extend a fast. A free timer cannot decide whether fasting is safe for your body.

How people usually start

Begin near what you already do. Many people already go 10–12 hours overnight without calling it intermittent fasting. Stretching that toward 12–14 hours for several days, then considering 14–16 hours if it still feels manageable, is more sustainable than jumping to OMAD. If you have not picked hours yet, start with How to start fasting.

Early hunger often comes in waves, driven by habit and usual meal times, not only by “running out of energy.” Water and realistic expectations help. Severe symptoms are different: tap End Fast and take care of yourself.

A wrecked night of sleep, high stress, a hard training week, or illness can make the same hours feel easy one week and brutal the next. Shortening the window or taking a rest day is a reasonable choice.

Using this timer

MyFastingClock is a free online fasting timer. It counts elapsed time, including a stretch past a day if that already matches a plan you have. There is no time cap so the clock can match that plan. It does not mean longer is wiser.