12:12 Intermittent Fasting: How It Works

In 30 seconds

12:12 intermittent fasting means eating within a 12-hour window and fasting for the other 12 each day, for example from 8 am to 8 pm. In trials it led to modest weight changes, similar to other fasting schedules. It is the least restrictive daily window.

• 12:12 means a 12-hour eating window and a 12-hour fast each day, for example 8 am to 8 pm.
• Trials found modest weight and cardiometabolic changes, similar on average across fasting schedules.
• An earlier window improved glucose and blood-pressure measures in small, short trials; results vary.
• No schedule is proven best for everyone; your circumstances and adherence matter.
• Check with a clinician before trying fasting if you have diabetes, take medications, are pregnant, have an eating disorder history, or are a minor.

How does 12:12 work?

You eat during 12 hours of the day and fast for the other 12. If dinner ends at 8 pm, breakfast waits until 8 am, and most of the fast happens while you sleep.

The 12:12 schedule means you eat only during a continuous 12-hour window each day and fast for the other 12 hours.Source 22

A sample 12:12 day

1. 8 pm to 8 am, 12 hours

   Fasting

   No calories after dinner; the fast runs overnight.

2. 8 am to 8 pm, 12 hours

   Eating window

   Meals and 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

12 h

Eating window

12 h

Fast ends

8:00 AM

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

Open the fasting calculator

Will 12:12 help you lose weight?

It can, modestly, and about as much as other fasting schedules: trials find modest weight and cardiometabolic changes for some people.

Time-restricted eating schedules, including 12:12, can produce modest weight loss and small cardiometabolic changes for some people, similar on average to other fasting strategies.Source 11

A 2025 network meta-analysis of randomized trials found modest average effects on weight and some cardiometabolic risk factors across fasting strategies. Results depended on trial definitions, adherence and duration.Source 11

Is an earlier eating window better?

Possibly, for blood sugar and blood pressure, but the evidence is early. Small trials that moved calories earlier in the day saw better insulin and glucose measures, and the early vs late window guide covers the detail.

Earlier eating windows modestly improved insulin sensitivity, 24-hour glucose and some blood-pressure markers in small randomized trials, sometimes without weight loss.Source 33Source 44Source 22

A 2026 review of timing and window length found both can influence metabolic outcomes, but differences between trials do not establish one best schedule.Source 22

Short trials that concentrated calories earlier in the day improved insulin sensitivity, 24-hour glucose and some blood-pressure markers, sometimes without weight loss. They were small and brief: they hint, they don't settle.Source 33Source 44

What about autophagy? One of those trials also saw shifts in gene-expression markers linked to autophagy, a hint rather than a measurement.

Small, short human studies report gene-expression marker changes tied to autophagy with early time-restricted feeding, but they do not show when autophagy begins or measure it across the body.Source 44

How does 12:12 compare with other schedules?

There is no proven best schedule for everyone. If 12:12 feels comfortable and you want a longer fast, 14:10 and 16:8 shorten the window one step at a time.

No eating window or fasting schedule is proven best for everyone; individual circumstances, trial differences and adherence influence outcomes.Source 11Source 22

Who should check with a clinician first?

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

• 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.

• 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.

• Intermittent Fasting Schedule: Common Options Compared

  Compare intermittent fasting schedules: 12:12, 14:10, 16:8, 18:6, 20:4 and 5:2. Trials found similar average effects, so pick one you can keep.

• Fasting Before Blood Work: Water, Coffee and How Long

  Fasting before blood work isn't always needed. When it is, follow the lab: what counts as fasting, whether water and coffee are OK, and what to ask if you take medicines.

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 12:12 intermittent fasting?

12:12 means eating only during a 12-hour window each day and fasting for the other 12. It is time-restricted eating and usually easier than shorter windows.Source 22

Will I lose weight if I do 12:12?

Some people do, modestly. Trials show average, modest effects with 12-hour windows; your results depend on total calories, adherence and activity.Source 11

Is 12:12 better than 16:8?

Neither is proven better. Shorter windows can cut more calories for some people, but outcomes depend on adherence and individual response.Source 11Source 22

When should you place the 12-hour eating window?

Wherever it fits your life, with two caveats: earlier windows showed modest glucose and blood-pressure benefits in small, short trials, and your medical needs come first.Source 33Source 44Source 22

Is 12:12 safe for everyone?

For many healthy adults, a 12-hour fast is generally lower risk than longer fasts. People with diabetes, on certain medicines, pregnant or breastfeeding, under 18, or with a history of disordered eating should check with a clinician first.Source 11Source 22Source 55Source 66Source 77

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