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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​

  1. Pick protocol — 16:8, 18:6, 20:4, OMAD (23:1), 24h, 36h, custom.
  2. Set last meal time — Marks the start of the fast. Timer counts up from there.
  3. 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.)
  4. Notify on window open — Browser notification fires when eating window opens. Plus reminder before window closes if 16:8 or shorter.
  5. 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.

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.

Try it now​

The full intermittent-fasting-timer runs in your browser at https://ztools.zaions.com/intermittent-fasting-timer — no signup, no upload, no data leaves your device.

Open the tool ↗

Last updated: 2026-05-05 · Author: Ahsan Mahmood · Edit this page on GitHub