21-Hour Fast Starting at 8:00 PM: End Time Calculator
Enter the time you start and we'll tell you exactly when your 21-hour fast ends — plus when key milestones land along the way.
How to read your result
Once your fast ends at 5:00 PM, break it gently — water first, then protein and fiber rather than sugar. The milestones above are typical estimates; your body's exact timing varies with your last meal, activity, and sleep.
Common mistakes
Skip the math — let the app track it
Fast Goblin counts your fast live, alerts you at each milestone, and tells you the exact moment you hit your goal. No spreadsheet, no account, all on your iPhone.
This calculator-style page answers the timing question first, then shows how to track the same window in Fast Goblin.
End time: 5:00 PM
| Calculation | Result |
|---|---|
| Start time | 8:00 PM |
| Fasting duration | 21 hours |
| End time | 5:00 PM |
| Day | next day |
Calculation
8:00 PM + 21 hours = 5:00 PM (next day)
Example fasting day
For a simple example, start your timer at 8:00 PM, keep the fast going through the full 21 hours, and break it at 5:00 PM. If that window feels awkward, move the start time instead of changing the whole plan.
Common mistakes
- Counting from the wrong meal instead of the actual fast start.
- Forgetting whether the end time is same day or next day.
- Changing the plan every day before you know what timing works.
- Using longer fasts as a shortcut instead of building a repeatable routine.
Track it in Fast Goblin
Fast Goblin can save the calculation by letting you start the fast and see the end time automatically. No more checking the clock twice and still being unsure.
How Fast Goblin helps
Fast Goblin can save the calculation by letting you start the fast and see the end time automatically. No more checking the clock twice and still being unsure.
Questions
It ends at 5:00 PM the next day.
For overnight or multi-day fasts, yes. The page shows whether the end time falls on the same day or a later day.
Yes. Use the calculator index or set a custom timer in Fast Goblin.
Track it automatically.
Free on the App Store, private by design. Android coming soon.