What is 18:6 fasting?
18:6 fasting means about 18 hours without food and an eating window of about 6 hours. It is a longer fast and a shorter time in which to eat than 16:8. This page explains the pattern so you can recognize it. It is not a suggestion to start there.
Read this after shorter windows feel familiar. If you have not yet read 16:8 fasting and fasting schedules, start with those. Many adults never need to study 18:6 beyond knowing what the numbers mean.
How it differs from 16:8
The extra two fasting hours are not a small detail for everyone. They often remove a meal rather than trim a snack. A person who used noon to 20:00 may move to noon to 18:00, or to 13:00 to 19:00. Dinner becomes earlier, or lunch and dinner move closer together.
Six hours can fit two meals if they are planned. It fits poorly with a long workday that already delays food, plus a late social dinner. The risk is not the number itself. The risk is copying the number while the rest of the day stays the same, then spending the evening overly hungry or skipping food you needed.
A sample, labeled as an example only: first meal at 12:00, last meal finished by 18:00, then water, plain coffee, or plain tea until noon the next day. Shift that block earlier or later if you use the planner, and keep the “example” label on it.
Who usually reads this page
People land here after they have already used a shorter eating window and want to know what a tighter one changes. They may have questions about hunger late in the afternoon, or about whether coffee still “counts.” Those are learning questions. They are not a sign that 18 hours is the correct next step.
If your days are irregular, if you are new to fasting, or if you prefer more time to eat, a 12:12 or 14:10 description is the more useful reading. The quiz points toward learning pages with that kind of split. It will not say that you should do an 18:6 fast.
Drinks, meals, and hunger
The drink convention does not change because the fast is longer. Water, plain black coffee, and plain tea are the common choices. Calories or sweeteners may end the fast for many people. That remains a convention, not a medical rule. See what to drink while fasting.
The first meal still needs to be ordinary food you can sit down for. A short window sometimes tempts people to eat very fast or to arrive at the meal overly empty. How to break a fast argues for a normal pace instead.
Hunger late in an 18 hour gap can be stronger than hunger on a 14 hour gap. Waves of hunger are described in hunger while fasting. Feeling faint, confused, or unwell is a reason to eat and to get help if those feelings do not pass after eating. It is not a reason to “finish the 18.”
Reasons to keep the window gentler
Sleep loss, a hard training day, illness, a stressful week, or a meal you want to share can all be reasons to use a shorter fast or to skip the pattern for a day. Fasting and exercise is relevant here because a long gap plus a hard session is a lot to combine.
Another reason is medication or a medical condition. This page cannot clear 18:6 for anyone. The safety note below is the constraint, not a footnote.
Common errors with longer windows are collected in common fasting mistakes: treating the longer number as progress, ignoring thirst, and cutting the eating window so far that meals become frantic. None of that is required in order to understand fasting. The broader definition sits on what intermittent fasting is.
Safety
Safety. People who are pregnant, breastfeeding, under 18, have an eating disorder or a history of one, have diabetes or hypoglycemia, take medication, or have a heart, kidney, or other medical condition should talk with a healthcare professional before fasting. Stop a fast and get help if you feel faint, confused, or unwell.
More short answers are in the FAQ. A full printable version of the basics is the beginner guide.