12:12
- Eating window
- 08:00 – 20:00
- Next meal after the fast
- 08:00 · next day
12h fast · 12h eating window
Fasting window calculator
To eat at noon on a 16:8 schedule, stop eating by 8:00 PM the day before — an 8-hour eating window and a 16-hour fast.
Your plan
16:8: eat from 12:00 PM to 8:00 PM. Then fast from 8:00 PM to 12:00 PM next day.
Eating window12:00 PM – 8:00 PM
Fasting window8:00 PM – 12:00 PM (next day)
16h fast · 8h eating window
Free, no account, no app. This plan stays on your device unless you copy or share it.
Keep this plan
Save this selected window on this device or export it once to your calendar. It never repeats automatically.
Local only. No account, sync, or recurring calendar event.
Fit a schedule to your day
Add your wake, sleep, and meal times to get a few practical fasting windows.
Routine planning only, not medical advice.
Suggested windows
16:8
Eating window: 12:00 PM – 8:00 PM
Fasting window: 8:00 PM – 12:00 PM (next day)
Matches your meal times14:10
Eating window: 11:00 AM – 9:00 PM
Fasting window: 9:00 PM – 11:00 AM (next day)
Close to your meal times18:6
Eating window: 1:00 PM – 7:00 PM
Fasting window: 7:00 PM – 1:00 PM (next day)
Close to your meal times
Compare schedules at the same meal time
Keep your first or last meal fixed and compare clock times. Choosing an option applies it to the calculator above.
14:10
- Eating window
- 10:00 – 20:00
- Next meal after the fast
- 10:00 · next day
14h fast · 10h eating window
16:8
- Eating window
- 12:00 – 20:00
- Next meal after the fast
- 12:00 · next day
16h fast · 8h eating window
Planning arithmetic only. These options do not rank health benefits or measure your body. Applying a choice does not save a plan or start the timer.
Try a worked example
Apply an example to the controls above, then change it to fit your own meal times. The next-day label appears only when the interval crosses midnight.
12:12: last meal at 20:00
Next meal after the fast: 08:00 · next day
16:8: last meal at 20:00
Next meal after the fast: 12:00 · next day
14:10: last meal at 22:00
Next meal after the fast: 12:00 · next day
16:8: last meal at 02:00
Next meal after the fast: 18:00
Plan selected dates
Choose a starting calendar date, then select which of the seven calendar days to plan. All days are initially unplanned. This sheet does not prescribe increasing fasting hours.
Choose a first date to open seven optional dates.
This sheet stays in this tab. It is not saved, sent to a server or added to your timer or history. Reloading clears it.
Work out exactly when to stop eating and when your eating window opens for any fasting schedule.
- Free core
- No account
- Local history
Planning estimates only — see methodology for phase sources. Not medical advice.
How the calculation works
Eating-window length = 24 minus fasting hours. From a last-meal time, add the fasting duration; from a first-meal time, add the eating-window duration. Clock times wrap at midnight.
Examples below use a last meal as the start of the fast. They show clock arithmetic, not advice about which schedule to choose.
These are local clock times, not measurements of metabolism. Check dates and times after travel or a daylight-saving change. A downloaded calendar file is a snapshot; later edits on this site do not update an imported event. The hourly calculator does not prescribe a 5:2 weekly meal plan.
Frequently asked questions
- What time should I stop eating on 16:8?
- On a 16:8 schedule with an 8-hour eating window, stop eating 8 hours after your first meal. For example, if you start eating at noon, stop by 8:00 PM, then fast for 16 hours until noon the next day.
- Does the calculator work for 18:6, 20:4 and OMAD?
- Yes. Choose any protocol and the calculator adjusts the eating window automatically — 6 hours for 18:6, 4 hours for 20:4, and about 1 hour for OMAD (23:1).
- Can I start the timer from the calculator?
- Yes. After you set your schedule, tap Start this fast to open the live timer with your protocol already selected.