Intermittent Fasting Timer

About the Intermittent Fasting Timer

Pick a fasting protocol — 12:12, 14:10, 16:8, 18:6, 20:4, OMAD (23:1) or a custom duration — set your start time, and watch a live circular countdown to the end of your fasting window. The tool also visualizes the metabolic stages your body moves through as the hours pass: glycogen depletion (~12h), ketosis (~16-18h), autophagy (~24h) and growth-hormone peaks (~48h). Your active fast is saved in the browser so you can close the tab and come back later.

What is intermittent fasting (IF)?

Intermittent fasting is an eating pattern where you cycle between periods of eating and periods of not eating (only water, plain coffee, plain tea — anything with calories breaks the fast). The most common pattern is 16:8 — you fast for 16 hours and eat all your meals within an 8-hour window. Research links IF to improved insulin sensitivity, increased autophagy (cellular cleanup), better metabolic flexibility, and modest weight loss for many people.

Which fasting protocol should I start with?

If you're new, start with 12:12 (just stop eating after dinner, skip late-night snacks) for a week or two so your body adjusts. Then try 14:10 — easy for most people if you push breakfast back a couple of hours. 16:8 is the most popular middle-ground and the one most studies use. Only move to 18:6, 20:4 or OMAD after months of practice — these require more discipline and aren't safe for everyone. Anyone pregnant, breastfeeding, underweight, with diabetes, or with a history of eating disorders should consult a doctor first.

Does coffee, tea, or water break the fast?

Plain black coffee, plain tea, and water do not break the fast — they have effectively zero calories and don't spike insulin meaningfully. Adding milk, cream, sugar, sweeteners, or anything with calories does break the fast. Most researchers consider artificial sweeteners (like stevia or aspartame) a grey area; if you're optimizing for autophagy, skip them. Bone broth has calories and should be considered a meal, not a fasting aid.

When does autophagy actually start?

Autophagy (the body's process of cleaning out damaged cell components) ramps up as insulin and amino acid levels drop. In human studies, measurable upregulation typically appears around 18–24 hours into a water-only fast and increases through 48–72 hours. The 'autophagy at 16 hours' claim popular on social media isn't well supported — at 16h most people are entering ketosis but autophagy is still climbing slowly. Don't fast extreme durations chasing autophagy without medical guidance; the marginal gains aren't worth the risk for most people.

Why does the timer show stages like 'glycogen burning'?

Your body works through predictable metabolic stages during a fast. First it burns the glucose in your blood (0-4h), then the glycogen stored in your liver (4-12h), then it switches to fat (12-18h) and produces ketones (16h+). Around 24h autophagy upregulates noticeably. The timer shows when each stage typically begins, based on Mattson 2017 and Anton et al. 2018 metabolic research — individual variation is large, so treat the times as a rough guide, not a precise prescription.

Can I do intermittent fasting every day?

Many people do 16:8 daily for years without issue. Studies show daily 16:8 is sustainable and produces modest weight loss + metabolic improvements in most healthy adults. Longer protocols (20:4, OMAD) are usually cycled — most practitioners do them 2-5 days per week rather than every day to avoid muscle loss, nutrient deficiencies, and metabolic adaptation. Listen to your body: if you feel weak, dizzy, irritable, or notice declining performance, ease the protocol or eat.

Will I lose muscle while fasting?

Short fasts (under ~36 hours) cause minimal muscle loss in healthy people, especially if you keep doing resistance training and hit your protein target during your eating window. Growth hormone actually rises during fasting (peaks around 48h, about 5× baseline), which is protective for muscle. Longer fasts (48h+) without resistance training do increase muscle catabolism. The key for IF practitioners: eat enough protein (0.7-1.0g per pound of bodyweight) during your eating window and lift weights 2-4 times a week.

Why does the timer keep running after I close the tab?

Your fasting state is saved in your browser's local storage. When you reopen the page, the tool reads your start time and computes how far through the fast you are. Nothing is sent to a server — the state lives only on your device. If you clear browser data, switch devices, or use incognito mode, the saved state is lost. To end a fast cleanly, hit the End Fast button so the localStorage entry is removed.

How do I use the eating window readout?

For daily time-restricted eating (TRE), your schedule has two halves: the fast and the eating window. The eating window is simply 24 minus your fast hours — 8h for 16:8, 6h for 18:6, 4h for 20:4. While the fast counts down, the tool shows the exact clock time your eating window will close ('eat by 8:00 PM'), so you can plan meals in advance. The moment the fast completes, it switches to a live count of how much eating time is left, then displays 'Eating window closed' when the next fast naturally begins. Extended fasts (36h+) don't have a daily eating window, so that readout is hidden for them.

What about whole-day protocols like 5:2 or alternate-day fasting?

This timer is built for time-restricted eating (TRE) — daily protocols measured in hours, like 16:8 or OMAD. Whole-day patterns work differently: 5:2 means eating normally five days a week and restricting calories (~500-600 kcal) on two non-consecutive days, while alternate-day fasting cycles a fasting day and a feeding day. Those are calendar-based rather than clock-based, so you'd track them on a weekly schedule. You can still use this tool on a 5:2 fasting day by running a long custom fast (e.g. 24-36h) to watch the metabolic stages, but the daily eating-window readout only applies to TRE.

How do I break a long fast safely, and what about electrolytes?

On fasts beyond 24-36 hours, electrolytes matter more than hunger. As insulin falls your kidneys excrete sodium, so supplement sodium (a few grams of salt in water), potassium, and magnesium to prevent headaches, cramps, fatigue and the so-called 'keto flu'. When breaking a 36h+ fast, refeed gently: start with something small and easy to digest (bone broth, a few nuts, or a light protein) and wait 15-30 minutes before a full meal — a large meal on an empty stomach can cause GI distress and, after multi-day fasts, dangerous refeeding-syndrome electrolyte shifts. If you take medication that must be taken with food, plan it for your eating window or talk to your doctor about timing; never skip prescribed medication to maintain a fast. Anyone with a medical condition should fast beyond 24h only under medical supervision.

Features

• 8 fasting protocols: 12:12, 14:10, 16:8, 18:6, 20:4, 23:1 (OMAD), 36h extended, or custom hours
• Live HH:MM:SS countdown with a circular progress ring
• Metabolic timeline showing 10 stages from fed state to stem-cell regeneration with their ETAs
• Auto-saves your fast to localStorage — close the tab, come back, the timer keeps running
• Pick a past start time if you forgot to start the timer at your last meal
• Highlights the current metabolic stage and how far past your goal you are
• Color-coded progress ring turns green when the goal is reached
• Works fully offline once loaded — no account, no tracking, no data leaves your device
• Mobile-friendly responsive layout
• Available in English, Spanish, Vietnamese, Portuguese and French