# Intermittent fasting windows explained *Guide · 2026-10-22 · https://undiet.app/guides/intermittent-fasting-windows* What the numbers in 14:10, 16:8, 18:6, 20:4, 5:2 and OMAD mean, what a day looks like on each, how the catalog rates their effort, and how to track a fasting period next to any other diet. ## What the two numbers mean In 16:8 the first number is hours fasting, the second is hours eating. A 16:8 day has an eight hour eating window, for example noon to 8pm, and nothing but water, black coffee or tea outside it. The same reading works for [14:10](https://undiet.app/diets/fasting-14-10), [18:6](https://undiet.app/diets/fasting-18-6) and [20:4](https://undiet.app/diets/fasting-20-4). The bigger the first number, the shorter the window. What you eat inside the window is not part of the method. That is why fasting sits in the catalog as a schedule rather than a diet. ## The daily windows, from easy to hard [14:10](https://undiet.app/diets/fasting-14-10) is the gentlest: a ten hour window such as 9am to 7pm, which for many people is close to how they already eat. The catalog rates it low effort. [16:8](https://undiet.app/diets/fasting-16-8) is the most common. It usually means skipping breakfast or dinner, and people report that mornings are the hard part at first, then routine. [18:6](https://undiet.app/diets/fasting-18-6) and [20:4](https://undiet.app/diets/fasting-20-4) shorten the window to six and four hours. Both are rated high effort because they take a real bite out of a social day. [OMAD](https://undiet.app/diets/fasting-omad), one meal a day, is the shortest window of all. It is a single sitting, and the catalog lists it as hard. ## The weekly patterns [5:2](https://undiet.app/diets/fasting-5-2) is a different shape: five ordinary days, and two non consecutive days kept very low, around 500 to 600 kcal as commonly described. [Alternate day fasting](https://undiet.app/diets/fasting-adf) turns that into every other day. [Eat stop eat](https://undiet.app/diets/fasting-eat-stop-eat) uses one or two full 24 hour fasts a week with ordinary eating in between. Weekly patterns leave most days untouched, which some people find easier and others find harder, because the low days stand out. ## Early or late window [Early time restricted eating](https://undiet.app/diets/fasting-etre) puts the window early in the day, for example 8am to 4pm, and skips dinner instead of breakfast. Which end of the day you cut is mostly a question of your life. Family dinners push the window late; early starts and quiet evenings push it early. ## What a fasting day looks like Pick the window, write it down, and keep the same hours most days. Water, black coffee and plain tea are the usual exceptions outside it. Most people report the first week as the adjustment, and that hunger at the usual mealtimes fades once the routine settles. The catalog page of each protocol carries the same note in neutral words. ## Tracking a fasting period In Undiet a fasting protocol is marked like any program, and it becomes a period on your timeline. You log weight and how the day felt, not what you ate. That matters with fasting, because the feeling is most of the story. A week of light days on 16:8 says something a scale alone does not. If you move from 16:8 to 18:6, or back to 14:10, each stretch stays as its own period, so you can see what each window did for you. ## Before you start Fasting is not for everyone, and the catalog does not say who it is for. Talk to your doctor if you take medication, are pregnant or have a condition that depends on regular meals. Not sure which window fits? [Find my diet](https://undiet.app/find-my-diet) asks five questions and narrows the catalog, including the fasting entries, to a shortlist. ## Programs in this guide - [Fasting 14:10](https://undiet.app/undiet/diets/fasting-14-10.md): All intake inside a consistent 10 hour window with a 14 hour overnight fast. - [Fasting 16:8](https://undiet.app/undiet/diets/fasting-16-8.md): Less a diet than a schedule: eating is kept within a set window (a common one is 8 hours). What you eat is up to you. - [Fasting 18:6](https://undiet.app/undiet/diets/fasting-18-6.md): A 6 hour eating window, studied as 1pm to 7pm. - [Fasting 20:4 (Warrior)](https://undiet.app/undiet/diets/fasting-20-4.md): A 4 hour eating window, studied as 3pm to 7pm; the Warrior Diet branding itself was never trialled. - [OMAD](https://undiet.app/undiet/diets/fasting-omad.md): One meal a day: the most extreme common fasting window. Demanding and not for everyone. - [Fasting 5:2](https://undiet.app/undiet/diets/fasting-5-2.md): Eat normally five days a week, keep calories very low on two non-consecutive days. - [Alternate Day Fasting](https://undiet.app/undiet/diets/fasting-adf.md): A 24 hour zero calorie fast on alternate days, in its strict form. - [Eat Stop Eat](https://undiet.app/undiet/diets/fasting-eat-stop-eat.md): One or two full 24 hour fasts per week, dinner to dinner. - [Early Time Restricted Eating](https://undiet.app/undiet/diets/fasting-etre.md): An eating window moved to the front of the day, studied as 7am to 3pm. More guides: https://undiet.app/undiet/guides.md. Find my diet in five taps: https://undiet.app/find-my-diet. Free on iPhone (https://apps.apple.com/app/id1490849895) and Android (https://play.google.com/store/apps/details?id=be.krnic.undiet). Undiet describes programs and records what you log. It does not give medical advice. --- Any diet. No calorie counting. Your weight, your effort and every diet you try, on one timeline. Undiet is a tracking companion, not a medical service. For people aged 16 and over. Made by Krnic CommV, Gent, Belgium. Contact: undiet@krnic.be. Privacy: https://undiet.app/privacy · Terms: https://undiet.app/terms · Delete your account: https://undiet.app/delete-account · Support: https://undiet.app/support