⏳ Fasting Timer
Set a target fasting duration and press start to track elapsed and remaining time with a ring-style progress display. Adjust the target freely to match popular fasting schedules like 16:8 intermittent fasting.
How to use
- Use the slider to set your target fasting duration (4-48 hours).
- Press "Start Fast" as soon as you finish eating.
- The ring and remaining time update in real time, and the timer shows "Complete" once the target is reached.
How the calculation works
This timer records when you start fasting and shows the elapsed time and the time remaining to your goal, updated every second. Remaining = goal − (now − start time) Elapsed time is calculated from the difference between the start time and the current time rather than by counting seconds, so it stays correct even if your phone sleeps or you close the tab and come back later. The start time and goal are saved in your browser (localStorage), and the start time and planned end time are shown. The ring shows elapsed ÷ goal. Goals can be set from 4 to 48 hours.
Worked example
Finish dinner at 8 pm and start a 16-hour fast Planned end: noon the next day Checking at 7 am the next morning Elapsed: 11:00:00 Remaining: 5:00:00 Ring: 11 ÷ 16 ≈ 69% With 16:8, the 16-hour fast is followed by an 8-hour eating window, here noon to 8 pm.
Things to be aware of
- If you are being treated for diabetes or another condition, are pregnant or breastfeeding, are a growing child, or have a history of eating disorders, consult a doctor before fasting.
- Keep drinking water while fasting. Stop immediately if you feel dizzy or unwell.
- Data is saved only in this browser and is not shared with other devices or browsers.
FAQ
What is 16:8 intermittent fasting?
A popular intermittent fasting schedule where you fast for 16 hours and eat within an 8-hour window each day. You can set the target to 16 hours in this tool to follow it.
Is my progress saved if I close the tab?
Yes. When you start a fast, the start time and goal are saved in this browser, so if you reload the page or close the tab, the timer picks up from the elapsed time next time you open it. Pressing "End fast" clears the saved data. It is stored only in your browser and never sent anywhere.
What should I know before starting a fast?
If you have a medical condition, are pregnant or breastfeeding, or are still growing, consult a doctor before fasting. Stop immediately if you feel unwell.