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20:4 intermittent fasting

A restrictive daily schedule with 20 hours without eating and four hours for meals. It is not a progression target or a recommendation for beginners.

20h

Fast

4h

Eating window

Start 20:4 timer

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  • No account
  • Not medical advice

By FastWindowTimer · Published: 2026-06-21 · Content updated: · Not individually medically reviewed — see editorial policy

Example schedule

  1. Eating window opens at 4:00 PM

    First planned meal time.

  2. Eating window closes at 8:00 PM

    Last planned meal time.

  3. Fast until 4:00 PM the next day

    20-hour fasting window begins.

Planning considerations

  • A 16:00–20:00 window leaves four hours for all meals.
  • Use this page to compare timing constraints; suitability requires your own circumstances and, when needed, professional advice.

Practical tradeoffs

Practical use

  • Makes the time constraint explicit so you can see conflicts before trying it.

Constraints

  • A four-hour window leaves little flexibility and may make eating adequately difficult.
  • Do not alter prescribed medication or ignore symptoms to complete a window.

Sources

  1. 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:

  2. 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

Should I progress from 16:8 to 20:4?
There is no required progression. If a narrow window makes eating rushed or causes symptoms, widen it or stop. More time fasting is not automatically a better outcome.
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.

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