Intermittent fasting schedules compared

Each intermittent fasting schedule is named after the way it splits a day or a week. Read 16:8 as sixteen hours without food followed by eight hours with it, and the pair always totals 24. In 5:2, the numbers are days: five ordinary days and two low-calorie ones. Choose a daily schedule below and enter the time you finished eating to see your window.

Every intermittent fasting schedule in one table

The daily schedules differ only in how long the fast lasts. The weekly ones work differently, because the fast days still include some food.

Schedule	Fasting	Eating	Who it tends to suit	Full page
12:12	12 hours, mostly overnight	12 hours	First-timers and people who snack late in the evening	14:10 page (12:12 is its first step)
14:10	14 hours	10 hours	People who want to keep three meals	14:10 schedule
16:8	16 hours	8 hours	People who can drop breakfast or an evening meal	16:8 schedule
18:6	18 hours	6 hours	Two-meal eaters who already find 16:8 easy	18:6 schedule
20:4	20 hours	4 hours	Experienced fasters; demanding, and protein is hard to fit in	20:4 schedule
OMAD	About 23 hours	About 1 hour	The strictest daily option; one plate must hold the day’s food	OMAD guide
5:2	2 days a week at about 500 kcal (women) or 600 kcal (men), a popular convention	5 normal days	People who prefer two hard days to a daily rule	5:2 planner
4:3	3 non-consecutive days a week at about a fifth of usual food	4 normal days	People who want fast days and can manage three a week	5:2 planner
Alternate-day	Every other day at about a quarter of daily energy needs	The days between	People who can cope with frequent fast days	Weekly fasting guide

The 4:3 and alternate-day amounts come from year-long trials of those methods. Splits such as 15:9, 17:7 and 19:5 follow the same arithmetic. Add the fasting hours to the time you finished eating, and the window runs for the rest of the 24 hours.

How many hours is intermittent fasting?

No health body sets a minimum number of hours. The common daily schedules run from 12 hours of fasting up to about 23 on one meal a day. Our timer treats 12 hours as a completed fast, and that threshold is our own rule.

The hours change what fuel your body uses. In human studies, the body shifts to burning more fat and making ketones somewhere between 12 and 36 hours after eating. Your own point in that span turns on the size of your last meal and on how much you move. There is no human evidence for a set hour when autophagy (cell recycling) begins, so no schedule can promise it.

Fasts that run past a full day are a different undertaking from the schedules on this page. Get a doctor’s advice before you try one.

Which intermittent fasting schedule is best?

Total calories matter more than the schedule for weight loss. Fasting has been tested against ordinary calorie cutting in a year-long trial and in a 2025 review that pooled 99 trials. With calories matched, the results were broadly similar. The review called it “some indication”, so that evidence is moderate.

A few trials compared methods directly:

• In the 2025 review, people on alternate-day fasting lost roughly 1.3 kg more than those cutting calories daily. Most of that gap came from trials under 24 weeks.
• In one 12-month trial, 4:3 fasting lost about 2.9 kg more than daily calorie cutting with the same weekly deficit. Both groups also had a full weight-loss programme.
• Over 8 weeks, adults with obesity lost about 3% on either a 4-hour or a 6-hour daily window.

The 4:3 and window-length results each come from a single trial, so that evidence is early. We found no trial showing one schedule is best for blood sugar, autophagy or a longer life. In practice, the best intermittent fasting schedule is the one you can keep on most days without feeling unwell.

The schedule chooser turns this into a single suggestion. Its six questions cover your routine, your meals and your current overnight gap.

The best time of day to eat

There is a little evidence on clock times. Eleven adults with overweight tried eating from 8 am to 2 pm for 4 days in one study. Their average 24-hour blood sugar came out slightly lower than on an 8 am to 8 pm schedule. That is early evidence from one very short study.

A later window has been tested too. In a 12-week trial of 116 adults, eating from noon to 8 pm gave no more weight loss than three meals spread through the day.

So place the window where it does the least damage to your day. If evening meals with family matter, skip breakfast and eat from midday. If you wake up hungry, an earlier window that ends in the late afternoon may be easier. Either way, most of the fast falls overnight while you sleep.

Switching between schedules

You can change schedules, and you can change your times from day to day. In the calculator, each window starts from the time you finished eating that day. A late dinner pushes the next window later.

To step up, move your first meal an hour or two later and stay there until it feels routine. A common path is 12:12, then 14:10, then 16:8. Going further is optional. If a week goes badly, drop back one step. The first weeks are covered step by step in our starter guide.

Moving from a daily window to a weekly method works differently. On 5:2 you eat normally on most days and keep two days low in calories. The 5:2 planner marks your fast days and adds them to your calendar. For a side-by-side look at 16:8, 18:6, 20:4 and OMAD, read our comparison of daily windows.

When to skip a fasting schedule

Some people should not follow any of these schedules without a doctor’s advice first. That includes anyone pregnant, breastfeeding or under 18. It also includes anyone frail or recovering from illness. For anyone who has had an eating disorder or has one now, or is underweight, we advise against these schedules.

Diabetes needs the same care. Insulin and sulfonylureas carry a risk of a hypo (low blood sugar) on days you eat less. Anyone taking them needs a doctor’s plan first. If a medicine has to be taken with food, plan your window around it with your doctor. Never skip a dose to protect a fast.

Put your schedule on paper or on a timer

The printable schedule template turns your schedule and usual last meal into one or four weeks of times to print. The fasting timer tracks each fast as it happens, works offline and keeps your streak on your device.