Intermittent Fasting Timer
Track a 16:8, 18:6, 20:4 or OMAD fast with a live timer, see when your eating window opens and closes, and plan a daily schedule.
The interactive tool loads here when JavaScript runs.
About this toolWhat is the Intermittent Fasting Timer?
The Intermittent Fasting Timer counts the hours since your last meal and shows how long is left until your fast ends and when your eating window closes. Pick a pattern (12:12, 14:10, 16:8, 18:6, 20:4, one meal a day, or a custom length up to 72 hours), press Start fast now or enter the time you stopped eating, and the progress ring updates every second.
When you end a fast it goes into a short history with its length and whether it met the goal. A separate planner turns a chosen first-meal time into a daily schedule, for example eating from 12:00 to 20:00 and fasting until noon the next day.
The timer and history are kept in your browser's local storage on this device only. Nothing is sent to a server, so clearing site data resets them.
- Live countdown with a progress ring
- 12:12, 14:10, 16:8, 18:6, 20:4, OMAD or custom up to 72 hours
- Fast end and eating window close times
- History of recent fasts on this device
- Daily schedule planner with a 24-hour bar
- No account; data stays in your browser
How to use the Intermittent Fasting Timer
- Choose a pattern, or Custom and type the fast length in hours.
- Press Start fast now when you finish eating, or set the date and time of your last meal if you started earlier.
- Watch the ring and the countdown. When the fast ends, the page counts down to the close of your eating window.
- Press End fast when you eat again. The fast is saved to Recent fasts with its length.
- Use the planner to choose a first-meal time and see the matching last-meal and fast-end times for every day.
Worked examples
16:8 from an evening meal
Input
Last meal finished 20:00, pattern 16:8
Output
Fast ends 12:00 tomorrow; eating window closes 20:00 tomorrow
Most of a 16-hour fast passes overnight, which is why 16:8 with a noon-to-8pm window is the most common choice.
18:6 planner
Input
Eating window opens 11:00, pattern 18:6
Output
Last meal by 17:00, fast until 11:00 next day
A 6-hour window ending in the late afternoon follows the early time-restricted eating pattern used in some studies.
Custom 36-hour fast
Input
Custom 36 hours, started 19:30 Sunday
Output
Fast ends 07:30 Tuesday; no daily eating window
For fasts of 24 hours or longer the page shows only the end time, and the planner explains there is no daily window.
Background and insight
Intermittent fasting covers several patterns. Time-restricted eating, the kind this timer tracks, limits food to a window each day: 16:8 means a 16-hour fast and an 8-hour window. Other forms include alternate-day fasting and the 5:2 diet, with two low-calorie days a week. The 2019 New England Journal of Medicine review by Rafael de Cabo and Mark Mattson describes the metabolic switch that happens as the body runs down liver glycogen and relies more on fat and ketones, typically after 12 hours or more without food.
The evidence for weight loss is less dramatic than the popularity suggests. In the TREAT trial (Lowe and colleagues, JAMA Internal Medicine, 2020), 116 adults following 16:8 for 12 weeks lost 0.94 kg against 0.68 kg in the control group, a difference that was not significant. A 12-month trial in the New England Journal of Medicine (Liu and colleagues, 2022) found that adding an 8-hour eating window to calorie restriction gave no extra weight loss over calorie restriction alone. Fasting seems to work mainly by making it easier for some people to eat less.
Timing may matter apart from calories. In a small, tightly controlled study (Sutton and colleagues, Cell Metabolism, 2018), men with prediabetes who ate within 6 hours ending by mid-afternoon improved insulin sensitivity and blood pressure without losing weight. Early windows suit the body clock better than late-evening eating, but long-term evidence is still limited.
Common use cases
Daily 16:8 or 18:6 routine
Start the timer after dinner and check in the morning how long is left.
Planning around work or training
Use the planner to fit the eating window around meals with family or a workout.
Keeping a simple log
See the last few fasts and whether you reached the target length.
Trying a longer fast once
Set a custom length to see exactly when a 24 or 36-hour fast would finish.
Tips and limitations
- Water, black coffee and plain tea are generally treated as fine during a fast; anything with calories ends it.
- Start with 12:12 or 14:10 and lengthen slowly. Headaches and irritability in the first week usually ease.
- What you eat in the window still matters. Fasting does not offset large or very processed meals.
- Fasting is not advised in pregnancy or breastfeeding, for under-18s, after an eating disorder, or with diabetes treated by insulin or sulfonylureas without medical supervision.
- The timer keeps running when you close the page because it stores the start time; it does not send notifications.
Frequently asked questions
What is 16:8 intermittent fasting?
You fast for 16 hours and eat within an 8-hour window each day, for example from 12:00 to 20:00. It is the most studied and most popular time-restricted eating pattern.
Does black coffee break a fast?
Black coffee, plain tea and water have almost no calories and are generally allowed. Milk, sugar, juice or anything with meaningful calories ends the fast.
Does intermittent fasting help with weight loss?
It can, mainly because a shorter window helps some people eat less. Controlled trials such as TREAT (2020) and a 12-month NEJM trial (2022) found little or no extra weight loss compared with simply cutting calories.
Which fasting window is best?
The one you can keep. Early windows that end in the afternoon have shown metabolic benefits in small studies, but 12:00 to 20:00 is easier for most people socially.
Who should not try intermittent fasting?
People who are pregnant or breastfeeding, under 18, have a history of eating disorders, or have diabetes on insulin or sulfonylureas should not fast without medical advice. The same applies to anyone on medicines that must be taken with food.
Will the timer keep running if I close the page?
Yes. It stores the start time in your browser, so the count is correct when you return on the same device and browser. It does not send alerts.
What is OMAD?
One meal a day, usually a 23-hour fast with about an hour to eat. It is a demanding pattern, and getting enough protein and nutrients in one meal takes planning.
Is there an in-depth guide to the Intermittent Fasting Timer?
Yes. “Intermittent Fasting Schedules: 16:8, 18:6, OMAD and the Evidence” covers the background, how it works, common pitfalls and worked examples. Read the full guide.
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