18:6 Intermittent Fasting: How It Works

In 30 seconds

18:6 intermittent fasting compresses the day’s eating into about six hours and extends the fast to roughly 18, for example eating from 1 pm to 7 pm. In trials, schedules like 18:6 produced modest weight changes, broadly similar to other fasting approaches. It is more restrictive than 16:8, and a longer fast is not a required next step.

• 18:6 means about 18 hours of fasting and a 6-hour eating window each day, for example 1 pm to 7 pm.
• Trials found modest weight and cardiometabolic changes, broadly similar across fasting schedules.
• Earlier windows improved insulin sensitivity and 24-hour glucose in small, short trials; results vary.
• 18:6 is a choice, not a required next step after 16:8; pick the schedule you can keep, and check with a clinician first if you take medicines or have a medical condition.

How does 18:6 work?

You eat within about six hours and fast for the other 18. If your last meal ends at 7 pm, the next one waits until 1 pm, and most of the fast happens overnight.

18:6 is a time-restricted eating schedule that confines a day's eating to about six hours and fasting for the remaining ~18 hours.Source 22

A sample 18:6 day

1. 7 pm to 1 pm, about 18 hours

   Fasting

   No calories after an early dinner; the fast runs overnight and into the next day.

2. 1 pm to 7 pm, about 6 hours

   Eating window

   Two regular meals and any caloric drinks stay inside the window.

Try a schedule

Example times. Nothing is saved.

Schedule

12:1214:1016:818:620:4

Last meal

8:00 PM

Fasting

18 h

Eating window

6 h

Fast ends

2:00 PM

Eating window: 2:00 PM to 8:00 PM. Hours on a clock are not a measurement of your body.

Open the fasting calculator

Will 18:6 help you lose weight?

About as much as other fasting schedules. Trial syntheses find modest weight and cardiometabolic effects across fasting approaches, broadly similar when differences in weight change are accounted for.

Network meta-analysis of randomized trials indicates that intermittent fasting schedules, including 18:6, produce modest weight and cardiometabolic effects that are broadly similar across approaches when differences in weight loss are accounted for.Source 11

A network meta-analysis of randomized trials compared intermittent-fasting strategies on weight and cardiometabolic risk factors. It found modest, broadly similar effects across time-restricted and other approaches, with results depending on trial definitions, adherence and duration.Source 11

Is an earlier eating window better?

Possibly, for blood sugar, but the evidence is early. Small trials that placed the window earlier saw better insulin sensitivity and 24-hour glucose, sometimes without weight loss; the early vs late window guide covers the detail.

Small, short controlled trials of early time-restricted feeding found improved insulin sensitivity and lower 24-hour glucose even without weight loss, suggesting the timing of the window can affect glucose regulation in some people.Source 33Source 44

Short controlled trials of early time-restricted feeding reported better insulin sensitivity and lower 24-hour glucose independent of weight loss. They were small and brief, so they hint rather than settle long-term effects.Source 33Source 44

18:6 or 16:8: which fits you?

The one you can keep. Six eating hours make adequate meals and social dinners harder, and studies of timing and window length are too heterogeneous to crown one schedule. If 18:6 is not sustainable, step back to 16:8 or 14:10; a longer fast is not a required next step.

Studies of timing and eating-window duration are heterogeneous; they do not establish one universally optimal schedule and inherit differences in how interventions and populations were defined.Source 22

Who should check with a clinician first?

Meal timing can change blood-glucose patterns and interact with medicines.

People with diabetes, those taking glucose-lowering or other timing-sensitive medicines, pregnant or breastfeeding people, minors, and people with current or past eating disorders should consult a clinician before starting 18:6, because timing can affect medication response and metabolic control.Source 11Source 22

Talk to a qualified health professional before fasting if you are pregnant or breastfeeding, under 18, living with or recovering from an eating disorder, have diabetes, take insulin or a medicine affected by meal timing, are an older adult, or are acutely ill. Do not change the dose or timing of any medicine without your clinician. See Blimbi’s safety guide.

Related guides

• 12:12 Intermittent Fasting: How It Works

  12:12 intermittent fasting pairs a 12-hour eating window with a 12-hour fast. See a sample day, what trials found and who should ask a clinician first.

• 14:10 Intermittent Fasting: How It Works

  14:10 intermittent fasting pairs a 14-hour fast with a 10-hour eating window. See a sample day, what trials found and how to pick your window.

• 16/8 Fasting: How It Works and How to Start

  16/8 fasting (also written 16:8) means about 16 hours of fasting and an 8-hour eating window. See a sample day, how to build up to it and what trials found.

• Can You Chew Gum While Fasting? Sugar-Free Gum Explained

  Gum with sugar ends a strict fast. Sugar-free gum is a grey area that fasting trials never tested. What's in it and who should check the label before they chew.

Next steps

• Find a fasting schedule for your day

  Answer 3 quick questions and get a fasting schedule to try, with times that fit your day.

• When does my fast end?

  See the time remaining and an educational timeline. Hours on a clock are not a measurement of your body.

• Take the fasting quiz

  A few questions about your day, then a gentle place to start.

• Intermittent fasting protocols

  Compare the common schedules side by side.

Frequently asked questions

What is 18:6 intermittent fasting?

18:6 is a daily time-restricted eating pattern that limits eating to roughly six hours and extends the fast to about 18 hours. It is one of several schedules studied in trials.Source 22

Will 18:6 help me lose weight?

No schedule guarantees weight loss. Trial syntheses show intermittent fasting schedules, including short windows like 18:6, often lead to modest weight changes; outcomes depend on total calorie intake, adherence and individual factors.Source 11

When should the six-hour eating window be?

Some small, short trials report better glucose and insulin outcomes when the window sits earlier in the day, but they were brief and small. Longer, larger trials are still needed, and the best timing may vary by person.Source 33Source 44Source 22

Does 18:6 start autophagy?

Short biomarker studies report changes in gene-expression markers related to cellular pathways, but they do not measure whole-body autophagy or establish when it starts. Precise timing claims for autophagy are not supported by the human data.Source 44

Is 18:6 safe if I have diabetes or take medication?

Check with your clinician first. Meal timing can change blood-glucose patterns and interact with glucose-lowering or timing-sensitive medicines, and monitoring or medication adjustments may be needed.Source 11Source 22Source 55

Sources

1. 1

   Intermittent fasting strategies and their effects on body weight and other cardiometabolic risk factors: systematic review and network meta-analysis of randomised clinical trialsZhila Semnani-Azad et al. BMJ, June 18, 2025.DOI: 10.1136/bmj-2024-082007 · PMID: 40533200Systematic review and meta-analysis

2. 2

   Effects of timing and eating duration of time restricted eating on metabolic outcomes: systematic review and network meta-analysisYu-En Chen et al. BMJ, January 21, 2026.DOI: 10.1136/bmjmed-2024-001071 · PMID: 41586347Systematic review and meta-analysis

3. 3

   Early Time-Restricted Feeding Improves Insulin Sensitivity, Blood Pressure, and Oxidative Stress Even without Weight Loss in Men with PrediabetesElizabeth F. Sutton et al. Elsevier BV, June 5, 2018.DOI: 10.1016/j.cmet.2018.04.010 · PMID: 29754952Human randomized trial

4. 4

   Early Time-Restricted Feeding Improves 24-Hour Glucose Levels and Affects Markers of the Circadian Clock, Aging, and Autophagy in HumansHumaira Jamshed et al. MDPI AG, May 30, 2019.DOI: 10.3390/nu11061234 · PMID: 31151228Human randomized trial

5. 5

   Fasting Safely with DiabetesMartin M. Grajower. National Institute of Diabetes and Digestive and Kidney Diseases, August 26, 2020.Official guidance

6. 6

   Weight gain in pregnancyNHS. NHS, July 6, 2022.Official guidance

7. 7

   Overview – Eating disordersNHS. NHS, January 23, 2024.Official guidance