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Free FastingCalculator

16-Hour Fasting Timer

One tap starts a 16-hour countdown from now, or backdate it to your actual last meal. When it completes, the 8-hour eating window counts down automatically.

The 16-hour rhythm

Sixteen hours is the most searched fasting duration because it pairs a full night's sleep with a skipped morning meal: fast from 8 PM, sleep 11 PM–7 AM, and by breakfast time you're already twelve hours in with four to go. The timer shows remaining time, elapsed time, percent complete, and the exact end time. The mid-morning stretch is where a visible countdown earns its keep, turning a vague "not yet" into "1 hour 40 minutes". If your evening ran late, edit the start rather than abandoning the fast: a 16-hour fast that starts at 9:40 PM is still a 16-hour fast, just one that ends at 1:40 PM.

Planning tomorrow's window instead of timing today's? Use the16:8 calculator first and start the timer from its result; the schedule transfers exactly, including the start time. The two tools share one calculation engine, so the countdown you watch and the window you calculated can never drift apart.

A 16:8 clock that respects your intelligence

Most 16-hour timer apps dress the countdown in stage badges ("fat burning begins", "autophagy unlocked") pinned to specific hours. The research doesn't support that precision: fasting physiology shifts gradually, and the timing varies with what and when you last ate, your activity, and your individual metabolism. So this clock shows what is true and skips what isn't. What you get instead of theater: a progress bar that means something, an eating-window countdown after completion so "when do I stop eating?" is always answered, and ahistory that accumulates your real numbers: average fast length, longest fast, how often you reach 16 hours. Over a month, that data answers the questions the badges only decorate.

Patterns people run with this timer

The daily 16:8 is the default, but the timer doesn't care about orthodoxy. Weekday-only fasters start it Sunday through Thursday nights and let weekends breathe. Every-other-day fasters alternate 16-hour days with unstructured ones. Shift workers run their 16 hours against anight-shift schedule where the "morning" stretch falls at 9 PM. All of these produce honest history: the tracker records what happened, theweekly planner shows the pattern you're aiming for, and nothing scolds you for the difference. If your real average turns out to be 14 hours, that's a fine schedule with a name, and acalculator of its own.

Common questions

How long is a 16-hour fast in practice?

From your last bite tonight to your first bite after noon tomorrow, typically. Finish at 8 PM and the timer runs to 12 PM the next day, with your night of sleep covering roughly half of it.

When should I start the 16-hour timer?

At your last meal. If you forgot, start it now and press "Edit start time" to backdate it to when you actually stopped eating. The countdown recalculates instantly.

What happens at hour 16?

The timer completes, records your session locally, and flips to an 8-hour eating-window countdown so you know when your next fast begins. We deliberately do not display hour-by-hour "metabolic stage" claims: exact biological timings vary between people and cannot be read off a clock.

Can I do 16 hours every day?

Many people run 16:8 daily; others keep it to weekdays or every other day. Whether it suits you is a personal and, in some cases, a medical question; see the safety note above. The timer and history simply record what you actually do, whichever pattern you choose.

Is this 16-hour timer free and account-free?

Yes. No signup, no subscription, no app store. It runs in your browser, stores your fasts on your device, and exports your history as JSON or CSV whenever you want it.

Does the countdown survive closing the browser?

Yes. The start time is stored as an absolute timestamp, so reopening the page shows the correct elapsed and remaining time even hours later or after a device restart.

What does 16 hours of fasting do?

Honestly: it structures your day so all eating fits an 8-hour window, which helps many people eat less overall, though average results in studies are modest and individual. Physiological changes during fasting develop gradually and vary from person to person; no specific switch flips at hour 16, and we won't pretend otherwise.

Can I use this as a 16:8 fasting clock for a different window?

Yes. The timer counts 16 hours from whenever your fast starts, so it works for any 16:8 placement: 12 PM–8 PM windows, 8 AM–4 PM windows, or a night-shift pattern. Pair it with the 16:8 calculator to pick the placement first.

Can I drink coffee or water while the 16-hour timer runs?

Water is generally considered compatible with fasting, and most 16:8 practitioners include black coffee and plain tea without resetting their timer. Anything with meaningful calories ends the fast for tracking purposes; if that happens, just press "Break fast" and the honest duration is recorded.

What is a 16-hour fast time chart?

A lookup of start-to-end pairs: 6 PM → 10 AM, 7 PM → 11 AM, 8 PM → 12 PM, 9 PM → 1 PM, 10 PM → 2 PM (always start time plus 16). The timer replaces the chart with your exact time, but the pattern is worth internalizing: every hour your last meal moves, your eating time moves with it.

How does the 16-hour timer compare with fasting apps?

Feature-for-feature on what matters (countdown, corrections, eating-window rollover, history), it matches paid apps, minus accounts, subscriptions, notifications-you-didn't-ask-for, and stage badges the evidence doesn't support. Reddit's recurring complaint about fasting apps is paying $20–50 a year for a timer; this one stays free because a timer is arithmetic.

Does the eating-window countdown start automatically?

Yes. The moment your 16 hours complete (or you press "Break fast"), the timer flips to the 8-hour eating window and counts down to your next fast, so "when do I stop eating?" always has a live answer without touching anything.