Intermittent Fasting Timer
Set your start time and protocol, then watch a live countdown to the end of your fasting window.
This timer runs entirely in your browser. Your start time is saved only on this device and nothing is uploaded.
How to use this tool
Pick the time you started fasting, or tap "Use current time" to set it to right now. Choose your protocol, such as 16:8 or 20:4, then press "Start fast". The tool shows your exact fasting end time and a live countdown that ticks every second. Your start time stays saved on this device, so you can close the tab and come back later and the countdown keeps going from where it should be. When the countdown reaches zero your eating window has begun.
How the fasting countdown works
Each protocol splits a 24 hour day into a fasting window and an eating window. The first number is how many hours you fast. For 16:8 you fast for 16 hours and eat within the remaining 8 hours. The timer adds the fasting hours to your start time to find the end time, then subtracts the current browser clock from that end time every second to show how much of your fast is left. Because it reads your device clock directly, the countdown stays accurate even if you refresh the page.
A real example
Say you finish dinner at 8:00 PM and choose the 16:8 protocol. The tool adds 16 hours to 8:00 PM, giving a fasting end time of 12:00 PM (noon) the next day. If it is currently 9:30 AM, the countdown reads 2 hours and 30 minutes remaining. At noon the countdown hits zero, and your 8 hour eating window runs until 8:00 PM that evening, when the next fast would begin.
Common questions
Does this intermittent fasting timer keep running if I close the tab?
Yes. Your start time is saved in your browser's local storage, so when you reopen the page the timer recalculates the remaining time from the current clock. The countdown does not need to stay open to stay accurate.
What is the difference between 16:8, 18:6, and 20:4?
The numbers are fasting hours to eating hours within a 24 hour day. 16:8 means 16 hours fasting and an 8 hour eating window, 18:6 means 18 hours fasting, and 20:4 means 20 hours fasting with a tight 4 hour eating window. Longer fasting windows are generally considered more advanced.
Can I track a fasting window that started yesterday?
Yes. Use the date and time picker to set any past start time. The timer will calculate your end time and show the correct remaining time, even if part of the fast has already passed.
Will it alert me when my fast ends?
The countdown switches to a clear "eating window" message when it reaches zero. Browser tabs cannot reliably play sounds in the background, so check the page when you expect your fast to end rather than relying on an alarm.
Is intermittent fasting safe for everyone?
This tool is for general education and tracking only, not medical advice. Intermittent fasting is not suitable for everyone, including some people who are pregnant, have diabetes, or have a history of eating disorders. Talk to a qualified healthcare professional before starting any fasting schedule.