Free online fasting timer
A free unlimited fasting timer for 16:8, OMAD, and open-ended fasts. No time caps. Not medical advice.
Free. No signup. Runs in this browser.
Start Fast with 16:8, OMAD, or Open on this page. The clock is the widget below the chips when JavaScript is on.
Protocol timers
Before you use this clock
This is a timer, not a clinician. The ring measures elapsed time. It cannot see your medicines, your last meal, or whether fasting is safe for you.
Do not start unsupervised if
You are pregnant or breastfeeding, under 18, underweight, or living with an eating disorder (now or in recovery). Diabetes, kidney disease, and medicines that lower blood sugar or blood pressure also move this out of “try a window” and into a conversation with a clinician who knows you.
End the fast if
- Dizziness on standing, confusion, fainting, chest pain, or severe weakness
- A tremor or dread that is not ordinary hunger
- You take glucose-lowering medicine and feel low
- Food distress shows up: panic, numbness, or a pull toward bingeing or purging
While the clock is running
Water is the default. Black coffee or unsweetened tea are optional. Extra salt is not a performance trick, and it is unsafe with some medicines and kidney disease.
Early hunger often arrives in waves around usual meal times. A wave that eases is common. A wave plus danger signs is a stop, not a dare.
Stage badges (ketosis, autophagy window, and the rest) follow approximate hours. They are not lab results and not a reason to add more time.
- What usually ends a fast
- Hydration & electrolytes
- Hunger comes in waves
- What the stages mean
- Health disclaimer
This timer will not pretend
Other fasting clocks sell a streak, a scale, or a stage that sounds like a lab. This one measures elapsed time. The stage names are there if you want them. You can ignore them.
No time cap is flexibility, not a dare
Open mode and multi-day presets exist so a long plan is not paywalled. They are not a ladder after 16:8. End Fast when you eat, or when you should stop.
The badge is a map, not a lab
Ketosis and Autophagy Window follow approximate hours. They do not read your blood. Two people at hour 16 can feel opposite things. The hard fact on this screen is the clock.
Wrong preset? Change mode. The start stays.
If you tapped 16:8 and meant Open, use Change mode under End Fast. Elapsed hours do not reset. The ring is a target, not a court.
No account to start. No scale. Ever.
Guest history stays on this device. Sign-in is only so the same log can live on another phone. We will not add a weight tracker. History is a map of fasts, not a kilogram board.
Questions this clock actually gets
Do I need to download an app?
No. Open this page and start. You can install it to the home screen later if you want a fuller-screen timer. That is optional.
What if I close the tab?
The running fast is saved in this browser on this device. Come back to the same site. Do not clear this site’s data. If you want the same fast on another phone, create a free account before you switch.
I started the wrong mode. Am I stuck?
No. Change mode while the fast is running. The start time stays. Only the goal changes. A longer goal can still chime later. A shorter goal you already passed will not ping you late.
I forgot to start the timer. Can I fix the start time?
Yes. While a fast is running, use Edit Start Time next to the started time. Set when you actually stopped eating. The clock jumps to that elapsed time. You cannot start in the future, and it cannot overlap a fast already in History.
Does the Ketosis badge mean I am in ketosis?
No. It means enough hours have passed on the educational timeline. It is not a ketone reading. Treat how you feel, and the stop rules, as more real than the label.
Can I keep going after the goal?
Yes. The goal is a bell, not a lock. Eat when your plan says eat. Use Open if you only want elapsed time and no target. Longer is not automatically better.
16:8 vs OMAD?
16:8 is an 8-hour eating window. OMAD is one meal. They are different loads, not a ranking. Pick either chip above, or use the dedicated 16:8 or OMAD pages if you already know which one you want.
Is it free?
Yes. No time cap and no subscription. Ads and optional donations keep it free.
Is this medical advice?
No. It is a clock and reading we wrote. It cannot see your medicines or your labs. If you are pregnant, under 18, underweight, or managing diabetes or an eating disorder, do not treat Start as clearance.
Fasting Library
- Fasting Library: Calm, structured education on intermittent and extended fasting: practice, history, human context, and research limits.
- Fasting Fundamentals: The main notes: what fasting is, safety, hunger, hydration, timer stages, schedules, and how to stop or eat again gently.
- How to make fasting easier: How-to notes for quieter hours: start near the overnight gap you already have, then water, an optional unsweetened mug, rest, and a window that fits a real day. Vinegar, salt stacks, and extra hours are not the method.
- Longer fasts: How-to notes for a stretch past a daily window: safety first, a plan, water, and an exit. A 72-hour challenge, stacked 16:8s, and a clinic at home are not the method.
- Very long fasts: For people who have already chosen a fast past 72 hours: signs that end it, why a clinician is the default, and a few known cases with their limits.
- Using the Clock: The timer as a tool: what a fasting clock is for, how to choose one, what this one does, and what it refuses.
- Everyday Fasting: Common questions from people actually using a window: what usually ends a fast, what to eat when you eat, first-week snags, real-life schedules, periods and hormones, why some people keep the hours, and alcohol on a daily window.
- Questions from the community: Short answers to questions people ask, with links to the notes that go into the detail. Not a salt recipe, not a plan for a week of water only, and not a plan for going without water.
- History of Fasting: From survival and ritual to medicine, protest, and modern wellness: what people did and believed, not diet prescriptions.
- Humans, Food & Feast–Famine: Meal patterns before and after agriculture, with hard limits on what prehistory can prescribe for modern schedules.
- What Research Suggests: How to read fasting studies, what TRE and related trials suggest, what headlines get wrong, how training sits with a window, what papers report as harm, and what is still unknown. Always with limits.
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