Pick a fasting goal, press Start fast after your last meal and watch the clock count toward it. The timer shows the time left, when your eating window opens, the typical fasting stage you are in, and saves every finished fast to a private history log.
Last updated:
Fasting goal
Ready to fast
00:00:00
of 16 h goal
Started
–
Goal reached at
–
Time left
–
Eating window
–
Forgot to press Start? Enter when you finished eating and the timer catches up.
Fasting stages
Timings are typical ranges reported for healthy adults and vary with your last meal, activity and metabolism. This is general information, not medical advice.
Fast history
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How to use the Fasting Timer
Choose a goal: 16:8 is selected by default. Tap 18:6, 20:4, OMAD, 36 h or Custom to change it, even during a fast.
Start the fast right after your last meal with Start fast. If you already stopped eating earlier, use Start at an earlier time and enter when you finished.
Watch your progress: the ring fills toward the goal, and the stage list shows where you are and when the next stage typically begins.
End the fast when you eat again. The fast is saved to your history with its duration and whether you met the goal.
Review your history: check your average, longest fast and streak, add a fast you forgot to track, or download everything as a CSV file.
Common fasting schedules
Time-restricted eating splits each 24-hour day into a fasting period and an eating window. The table shows what each schedule in the timer looks like if your last meal ends at 8:00 PM.
Schedule
Fast
Eating window
Last meal 8:00 PM → fast ends
Window closes
13 h (overnight)
13 h
11 h
9:00 AM
8:00 PM
16:8
16 h
8 h
12:00 PM
8:00 PM
18:6
18 h
6 h
2:00 PM
8:00 PM
20:4
20 h
4 h
4:00 PM
8:00 PM
OMAD (23:1)
23 h
1 h
7:00 PM
8:00 PM
36 h
36 h
none that day
8:00 AM, two days later
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The math is simple: goal time = start time + fast length, and the eating window is 24 h − fast length, counted from the moment the fast ends.
How the timer and stats work
The timer stores only your start time and goal, then compares them with the current clock every second, so it stays accurate when the tab sleeps or the browser restarts.
Goals met counts fasts whose duration was at least the goal you had set when you ended them. Current streak counts consecutive goal-met fasts, starting from the most recent.
The bar chart shows each of your last 14 fasts; dark green bars met their goal and the dashed orange line marks the goal for that fast.
Tips for an easier fast
Start with a 12 to 13 hour overnight fast and move to 16:8 once that feels easy.
Drink water through the fast. Hunger often passes within 15 to 20 minutes.
Break longer fasts with a normal, balanced meal rather than a very large one.
Keep the same schedule on most days; a regular routine usually feels easier than changing windows every day.
Frequently asked questions
What does 16:8 fasting mean?
16:8 means fasting for 16 hours and eating within an 8-hour window each day. For example, if you finish dinner at 8 PM, the fast ends at noon the next day and you eat between noon and 8 PM. 18:6 and 20:4 work the same way with longer fasts and shorter windows, and OMAD (one meal a day) is roughly a 23-hour fast with a 1-hour window.
When does a fast start?
A fast starts when you finish your last bite of food or drink anything with calories. Water, plain sparkling water, and black coffee or plain tea without milk or sugar are generally considered not to break a fast. If you forgot to press Start, set the start time to when you actually finished eating.
Does the timer keep running if I close the page?
Yes. The start time is saved in your browser, so the timer is calculated from the real clock and shows the correct elapsed time when you come back, even after restarting the device. The goal chime and notification only fire while the page is open in a tab.
When does ketosis start when fasting?
It varies a lot between people. Blood ketone levels typically begin to rise somewhere between about 12 and 24 hours without food, sooner if your last meal was low in carbohydrates or you exercised, and later after a large carbohydrate-rich meal. The stage list shows typical ranges, not measurements of your body.
What about autophagy?
Autophagy is the process cells use to break down and recycle their own components, and it is often linked to fasting. Much of the research on fasting and autophagy has been done in animals or cells, and there is no reliable way to know when it increases in a particular person, so this timer does not claim a specific hour for it.
Is my fasting data private?
Yes. Your active fast and history are stored only in this browser's local storage on this device. Nothing is uploaded and there is no account. Use Download CSV to keep a backup or move your log to a spreadsheet.
Who should not fast?
Fasting is not suitable for everyone. Children and teens, pregnant or breastfeeding people, anyone with a history of eating disorders, and people with diabetes or who take medication that affects blood sugar should talk to a doctor first. Stop fasting if you feel dizzy, faint or unwell.
Are all the tools on FreeToolCabin tested for quality and accuracy?
Yes! Every tool on our site undergoes automated Q/A testing in real browser environments to ensure high precision, correct output, and zero errors. If you happen to spot a bug or have a suggestion, please contact us at [email protected] and our team will review it right away.