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Free FastingCalculator

Fasting Timer

A fasting timer, clock, and tracker in one: live countdown, eating-window rollover, editable times for real life, and local history. Free, no account: everything stays on your device.

Built around how people actually fast

The most common timer complaint isn't about features: it's "I forgot to press start." Rigid timers turn that small slip into corrupted data or an abandoned day. This timer treats corrections as normal: edit the start time and it recalculates; break your fast early and it records the actual duration beside the target, neutrally; cancel a fast that isn't happening without ceremony. When a fast completes, the timer doesn't stop being useful: it flips to your eating window and counts down to the next fast, so the question "when does my window close?" always has a live answer on screen.

Under the hood it works the only way a reliable web timer can: your fast is stored as absolute timestamps on your device, and every displayed number is recomputed from the real clock. Close the tab for nine hours, reopen it, and the elapsed time is exactly right: no background process required, no drift, no battery cost.

Timer, clock, counter, tracker: one tool

People search for this tool under many names (fasting clock, fasting countdown, fasting counter, intermittent fasting tracker), and the differences matter less than apps pretend. A countdown tells you what remains; a clock places your windows in the day; a tracker remembers what actually happened. This page does all three: the live countdown with percent complete and exact end time, the schedule boundaries from whichevercalculatoryou started from, and automaticlocal historywith averages, medians, your longest fast, and target completion, plus optional streaks if you switch on Motivation Mode. What it deliberately isn't: a calorie counter, a recipe feed, a social network, or a subscription. Reddit threads about fasting apps repeat one sentence in different words, "I just need the timer", and that sentence is this page's entire specification.

Start from a calculation, not a guess

The timer is connected to every calculator on this site: run"When can I eat?", aprotocol calculator, or theschedule planner, press "Start fast" on the result, and the timer picks up the exact schedule, including a start time earlier than now if your last meal already happened. Quick-start buttons above cover the common protocols (12:12 through OMAD) and any custom duration up to 7 days for extended fasts. Whichever way you start, the same tested calculation engine defines the boundaries, so the timer never disagrees with the calculators.

Why we don't show "fat-burning stages"

Many fasting timers decorate the countdown with stage labels: ketosis at hour 12, autophagy at hour 16, each with an icon. It reads as science and tests as fiction: human research does not support assigning those transitions to precise clock hours, and the true timing varies with your previous meals, glycogen, activity, and individual metabolism. We'd rather show you three numbers that are actually true (elapsed, remaining, percent of target) than five that are decorative. If you want to read about what research does and doesn't establish on fasting physiology, oureditorial standardsexplain how we handle the evidence. Your timer should count time; it shouldn't tell stories.

Common questions

Is this fasting timer free?

Completely: no account, no subscription, no locked features. People searching for a "fasting timer online free" usually find apps that charge for a countdown; this one runs in your browser, free, forever, with your data stored on your own device.

Does the timer keep running if I close the tab?

Yes. The timer stores your fast start time as an absolute timestamp on your device, so elapsed time is recomputed from the clock whenever you return: refresh, close, or restart, nothing is lost.

I forgot to press start. Can I fix it?

Yes. Press "Edit start time" and enter when you actually stopped eating. The timer recalculates immediately. The same works in reverse: if you ate before pressing "Break fast", edit the end time afterwards.

What is the difference between a fasting timer and a fasting clock?

Different words for the same tool: something that shows where you are in your fasting cycle. This page gives you both views, a live countdown (timer) and your position in the 24-hour day with your window boundaries (clock), plus an eating-window countdown after the fast ends.

Is this also an intermittent fasting tracker?

Yes. Every completed fast is saved locally with its target and actual duration, and the history page turns that into averages, medians, longest fast, and completion rate: a full intermittent fasting tracker without an account or upload.

What happens when my fast ends?

The timer transitions into your eating window and counts down to your next fast, so you always know both boundaries. Your completed fast is saved to your local history automatically.

What if I break my fast early?

Press "Break fast" whenever you eat. The session records the actual duration next to the target, for example "14h 22m (1h 38m under target)". That is data, not failure; the history view reports averages, not shame.

Can the timer send notifications?

Not yet: browser notification behavior varies across platforms, and we would rather ship nothing than something unreliable. The calendar export covers the reminder use case today: your fast end and window close become normal calendar events with normal alerts.

Is my fasting history uploaded anywhere?

No. Sessions are stored in your browser (IndexedDB). You can export them as JSON or CSV, or delete everything, from the history page. Nothing about your fasting ever reaches a server.

Can I use this for 24, 36, or 48-hour fasts?

Yes. The custom duration accepts up to 168 hours, and the countdown works identically for extended fasts: absolute timestamps, editable start, honest recording. Extended fasting is also where the safety note stops being fine print; involve a professional if it applies to you.

Why doesn't the timer show fasting stages like other apps?

Because the hour-precise stage claims those apps display (ketosis at 12, autophagy at 16) are not supported by human research; the underlying physiology shifts gradually and varies by person. We show numbers that are true: elapsed, remaining, percent of your target, and your history over time.