12:12 intermittent fasting
An overnight schedule with 12 hours for meals and 12 without eating. It can describe an existing routine rather than a new diet.
12h
Fast
12h
Eating window
No app, no signup. The timer opens in your browser and keeps history on this device.
- No app
- No account
- Not medical advice
By FastWindowTimer · Published: 2026-06-21 · Content updated: · Not individually medically reviewed — see editorial policy
Example schedule
Eating window opens at 8:00 AM
First planned meal time.
Eating window closes at 8:00 PM
Last planned meal time.
Fast until 8:00 AM the next day
12-hour fasting window begins.
What research does—and does not—show about 12:12
These trials ask different questions: one directly includes 12:12, one uses a 12-hour control, and one tests 16:8. Read the actual comparison before applying a result to a different schedule.
| Study, design and participants | What was compared | What was measured or found | What this cannot establish |
|---|---|---|---|
| Sampieri et al. (2024) Eight-week randomized parallel trial with four groups. 41 metabolically healthy adults aged 18–65 without regular structured exercise. | 12:12 (08:00–20:00), 14:10, 16:8 and an unrestricted routine; participants were asked to maintain habitual calorie intake. | The authors reported no significant body-composition changes in the 12:12 group and no significant changes in measured blood markers across the groups. | Small groups and short follow-up; food intake and adherence were self-reported. This does not establish long-term effects, individual suitability or that a longer fast is better for the reader. |
| Sutton et al. (2018) Randomized crossover controlled-feeding trial; five weeks per schedule. Eight men with prediabetes completed both schedules. | An early six-hour eating window, with dinner before 15:00, versus a 12-hour eating window. The 12-hour window was the control. | The authors reported differences in insulin sensitivity and blood pressure favoring the early six-hour condition. | Small, specific group; timing and window length changed together. This does not show that 12:12 improves health, or recommend the six-hour condition to readers. |
| Lowe et al. — TREAT (2020) Twelve-week randomized trial; data from 116 adults were analyzed. Adults aged 18–64 with overweight or obesity; eligibility exclusions limit generalization. | Eating from 12:00 to 20:00 (16:8) versus three structured meals per day. The control was not a prescribed 12:12 schedule. | Weight change did not differ significantly between groups. Some additional measurements came from an in-person subgroup. | Tests 16:8, not the effects of 12:12. A nonsignificant difference does not prove that every schedule has identical effects. |
These studies do not establish a general health benefit of 12:12. A nonsignificant finding also does not prove that a schedule has no effect. This is a focused comparison, not a systematic review of every study. Clock-time examples do not predict personal health outcomes.
Planning considerations
- Breakfast and dinner 12 hours apart: 08:00–20:00.
- Use this page to compare timing constraints; suitability requires your own circumstances and, when needed, professional advice.
Practical tradeoffs
Practical use
- Allows breakfast, lunch and dinner without compressing meals into the afternoon.
Constraints
- Late snacks or an early breakfast shorten the overnight interval.
- Do not alter prescribed medication or ignore symptoms to complete a window.
Sources
- Sampieri et al. — Impact of daily fasting duration (Journal of Translational Medicine, 2024) (opens in a new tab)
What this source supports: Directly includes a 12:12 arm, an unrestricted comparator and the reported eight-week results.
What it cannot establish: Small, selected adult population; short duration and self-reported dietary intake and adherence limit generalization.
Source checked:
- Sutton et al. — Early Time-Restricted Feeding (Cell Metabolism, 2018) (opens in a new tab)
What this source supports: The trial compares early six-hour feeding with a 12-hour control in eight male completers with prediabetes.
What it cannot establish: Does not test 12:12 against an unrestricted routine or establish individual suitability; short, small crossover study.
Source checked:
- Lowe et al. — The TREAT Randomized Clinical Trial (JAMA Internal Medicine, 2020) (opens in a new tab)
What this source supports: Reports the 16:8 intervention, three-meal comparator, 12-week duration, analyzed population and between-group weight result.
What it cannot establish: Not a 12:12 efficacy trial; eligibility criteria and subgroup measurements limit generalization.
Source checked:
- Cleveland Clinic — What Is Intermittent Fasting? (opens in a new tab)
What this source supports: Describes daily time-restricted eating and the weekly 5:2 pattern. The example clock times on this page are arithmetic illustrations. It is background context, not a trial of this exact schedule.
What it cannot establish: Does not demonstrate that a longer fasting window is better or establish individual suitability.
Source checked:
- Cleveland Clinic — 6 Tips for Fasting Safely (opens in a new tab)
What this source supports: Discusses planning, hydration, medication and avoiding extreme fasting.
What it cannot establish: General clinical education, not approval of this exact schedule for the reader.
Source checked:
Frequently asked questions
- Does 12:12 require skipping breakfast?
- No. An 08:00–20:00 eating window includes breakfast. The notation only defines the interval; it does not prescribe calories or food choices.
- What does this schedule tell me about my body?
- Only the intended eating and fasting times. It does not measure insulin, ketones, autophagy, or the nutritional adequacy of your meals.
- What if the schedule does not fit my day?
- Choose a wider eating window or regular meal times. You do not need to compensate for a missed target by extending the next fast.