Intermittent Fasting Timer — Track 16:8, 18:6, 20:4, OMAD Windows
Track intermittent fasting windows: 16:8, 18:6, 20:4, OMAD, 24h. Live timer, stage milestones. Free, in-browser.
About Intermittent Fasting Timer
An intermittent fasting timer tracks the elapsed time in your current fast and the remaining time until your eating window opens — supporting common protocols (16:8, 18:6, 20:4, OMAD, 24-hour) and showing physiological stage milestones like "ketosis onset around hour 12–14" and "autophagy upregulation around hour 16+". The ZTools Intermittent Fasting Timer runs in the browser without an account, persists across page reloads, supports browser-notification alerts when the eating window opens or closes, and is for general lifestyle tracking — fasting is not appropriate for everyone (eating disorders, pregnancy, diabetes on insulin, etc.); consult a clinician before adopting it.
Use cases
- Daily 16:8 protocol tracking. The most common protocol. Eating window 12–8 PM; fast 8 PM–12 PM next day. Timer shows hours into fast and time to next meal.
- OMAD (one meal a day). 23-hour fast with a 1-hour eating window. Suits some people, not others. Timer keeps the schedule honest.
- Extended fasts (24h, 36h). Occasional 24- or 36-hour fasts — physiological stages spread over a longer period. Timer surfaces milestones and reminds to break the fast.
- Building consistency. Streak counter and weekly chart help establish habit. Consistency matters more than protocol choice for most people.
How it works
- Pick protocol. 16:8, 18:6, 20:4, OMAD (23:1), 24h, 36h, custom.
- Set last meal time. Marks the start of the fast. Timer counts up from there.
- Show stage milestones. ~hour 12: glycogen depletion; ~hour 14: ketosis onset; ~hour 16: growth-hormone rise; ~hour 24: autophagy increase. (All approximate; individual variation high.)
- Notify on window open. Browser notification fires when eating window opens. Plus reminder before window closes if 16:8 or shorter.
- Track streaks. Daily streak counter. Optional weekly chart of fast lengths.
Examples
Input: 16:8, last meal 8:00 PM
Output: Eating window opens 12:00 PM next day. Fast: 16 hours.
Input: OMAD, last meal 7:00 PM
Output: Eating window opens 6:00 PM next day. Fast: 23 hours.
Input: 24h fast, started 2026-05-04 19:00
Output: Ends 2026-05-05 19:00 — autophagy stage milestone reached.
Frequently asked questions
Is intermittent fasting for everyone?
No. Inappropriate for people with eating disorders, pregnant or breastfeeding, certain diabetes medications, low BMI, or some medical conditions. Consult a clinician first.
What happens during a fast?
Glycogen depletes in 12–14 hours; the body shifts toward fat oxidation and ketones. Growth hormone rises; insulin falls. Autophagy (cellular cleanup) increases at longer fasts. Most claims about specific timelines are approximate; human variability is high.
Will I lose weight on IF?
Only if the fast results in a caloric deficit. IF tools the schedule; it does not magically burn fat in a calorie surplus. Many find IF easier for adherence to a deficit because eating windows constrain calorie intake.
Can I drink during a fast?
Water, plain coffee, plain tea — yes. Anything with calories breaks the fast. Some traditions accept zero-calorie sweeteners; others do not.
How long until I see results?
Weight: 1–4 weeks. Other metabolic markers (insulin sensitivity): 2–8 weeks. Sustainability matters more than speed.
Can I exercise while fasting?
Yes for low-to-moderate intensity. High-intensity work suffers; some people split fasted-cardio in early window and resistance training near eating window.
Pro tips
- Hydrate during fasts — water, coffee, tea. Most "hunger" is mild dehydration.
- Pick a protocol you can sustain. 16:8 has the easiest adherence; OMAD is hardest.
- Eat enough during the eating window — chronic under-eating disguised as IF causes problems.
- For weight loss, intake during the eating window must hit a deficit — IF alone does not guarantee it.
- Consult a clinician before starting if you take medication, are pregnant, have diabetes, or have a history of disordered eating.
Reviewed by Ahsan Mahmood · Last updated 2026-05-05 · Part of ZTools.
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