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.
Work out exactly when to stop eating and when your eating window opens for any fasting schedule.
Your plan
- Eating window
- 12:00 – 20:00
- Fasting window
- 20:00 – 12:00 (next day)
16h fast · 8h eating window
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.
FastWindowTimer provides general information and planning estimates, not medical advice. Fasting isn't right for everyone — if you are pregnant, have a history of an eating disorder, have diabetes, or take medication, talk to a clinician first.