How the eating window is worked out
Time-restricted eating splits each day into a fasting period and an eating window. Pick your plan and the time of your first meal; the window closes a set number of hours later and the fast runs until the same time the next day.
Last meal = first meal + eating hours
Fast ends = last meal + fasting hours
Common intermittent fasting schedules
| Plan | Fasting | Eating window |
|---|---|---|
| 12:12 | 12 hours | 12 hours |
| 14:10 | 14 hours | 10 hours |
| 16:8 | 16 hours | 8 hours |
| 18:6 | 18 hours | 6 hours |
| 20:4 | 20 hours | 4 hours |
| OMAD (23:1) | 23 hours | 1 hours |
16:8 is the most common starting point. Many people start with 12:12 or 14:10 and lengthen the fast over a few weeks. The 5:2 approach is different: normal eating five days a week and much lower calories on two days, so it isn't a daily window.
Tips for a sustainable schedule
- Put the window where it fits your life, such as around training or family dinners.
- Keep it consistent — the same window most days is easier than a new one every day.
- Eat enough protein inside the window, especially if you lift.
- Water, black coffee and plain tea don't break a fast.
Who should not fast without medical advice
A fasting window is a schedule, not a treatment, and going long periods without food is not safe for everyone. Speak to a doctor before you start if you:
- take insulin or other glucose-lowering medication — fasting can cause hypoglycaemia, and doses may need adjusting;
- take any medication that has to be taken with food, or at fixed times;
- are pregnant, breastfeeding or trying to conceive;
- are under 18, or are an older adult at risk of losing muscle or weight;
- have or have had an eating disorder — rigid eating windows can make disordered eating worse;
- have diabetes, low blood pressure, a history of fainting, or are underweight.
Stop and get advice if fasting leaves you dizzy, shaky, unable to concentrate or preoccupied with food. Fasting is also not magic: in the trials cited below, time-restricted eating worked about as well as the same calories eaten across a normal day (Lowe et al., 2020; Liu et al., 2022). It helps if the schedule makes eating less food easier for you.
General fitness information, not medical advice. See the medical disclaimer.
Frequently asked questions
What does 16:8 mean?
You fast for 16 hours and eat all your meals within an 8-hour window, for example between 12:00 PM and 8:00 PM, every day.
Can I drink anything while fasting?
Water, black coffee and plain tea are usually fine because they have no calories. Anything with calories, including milk and sugar in drinks, breaks the fast.
Who should not try intermittent fasting?
Talk to a doctor first if you are pregnant or breastfeeding, under 18, have had an eating disorder, or take medication for diabetes or blood pressure. Fasting is a way to organise meals, not a medical treatment.
Sources
The formula on this page comes from the published work below. We check the numbers against the worked examples in these sources with automated tests, and re-read the page against them when we review it.
- Lowe DA, Wu N, Rohdin-Bibby L, et al. Effects of time-restricted eating on weight loss and other metabolic parameters in women and men with overweight and obesity: the TREAT randomized clinical trial. JAMA Intern Med. 2020;180(11):1491–1499. pubmed.ncbi.nlm.nih.gov/32986097/
- Liu D, Huang Y, Huang C, et al. Calorie restriction with or without time-restricted eating in weight loss. N Engl J Med. 2022;386(16):1495–1504. pubmed.ncbi.nlm.nih.gov/35443107/
General fitness information, not medical advice. Results are estimates; check with a doctor or qualified coach before major changes to diet or training. Formula and copy last reviewed 12 October 2026.