16:8, first meal at 12:00
Eat 12:00 to 20:00, fast until 12:00 the next day.
Intermittent fasting calculator
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Uses a daily time-restricted plan: you eat within one window and fast for the rest of the 24 hours. The 5:2 diet, with two low-calorie days a week, is a different method and is not timed here. Water, black coffee and plain tea are usually allowed while fasting.
Fasting plan
Your eating window
12:00 to 20:00
Eat between 12:00 and 20:00, then fast for 16 hours until 12:00 the next day.
- Eating hours
- 8 h
- Fasting hours
- 16 h
- Stop eating at
- 20:00
- Fasting hours a week
- 112 h
Each plan if your first meal is at 12:00
| Plan | Eat from | Last bite by | Fast for |
|---|---|---|---|
| 14:10 | 12:00 | 22:00 | 14 h |
| 16:8 | 12:00 | 20:00 | 16 h |
| 18:6 | 12:00 | 18:00 | 18 h |
| 20:4 | 12:00 | 16:00 | 20 h |
| OMAD (23:1) | 12:00 | 13:00 | 23 h |
Setting a fasting schedule that fits your day
Intermittent fasting limits when you eat rather than what you eat. The most common plan, 16:8, gives you an 8-hour window to eat and 16 hours without food, most of them while you sleep.
If your first meal is at 12:00, the 16:8 window runs to 20:00. On 18:6 it ends at 18:00, and on 20:4 at 16:00. Someone who prefers a late window can start at 19:30 on 18:6 and eat until 01:30, though most people find an earlier window easier to sleep with.
Pick a window that matches your work and family meals. Breakfast skippers usually do well with a noon start; people who eat with family at night may prefer 10:00 to 18:00 at weekends and later on weekdays.
Fasting helps some people eat less overall, but the calories you eat in the window still matter. If you feel dizzy, unwell or very hungry, shorten the fast. Check with a doctor if you take medicine for blood sugar or blood pressure.
Sources
What this calculator does not account for
- The 5:2 calorie method.
- What and how much you eat in the window.
- Medical needs such as diabetes medicine.
How this is calculated
Formula: Daily time-restricted eating
last meal =first meal + (24 − fasting hours)What the symbols mean
- fasting hours16 for 16:8, 18 for 18:6, and so on.
Good to know
- The fast runs from your last meal to your first meal the next day.
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Worked examples
Each example is worked out by the same code as the calculator above.
18:6, first meal at 19:30
Eat 19:30 to 01:30.
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The frame shows the tool only.
<iframe src="/embed/intermittent-fasting-calculator" title="Intermittent fasting" width="100%" height="720" style="border:0;max-width:42rem" loading="lazy"></iframe>Questions
How does 16:8 intermittent fasting work?
You eat within an 8-hour window and fast for 16 hours. With a first meal at 12:00, you eat until 20:00 and fast until noon the next day.
What can I drink while fasting?
Water, black coffee and plain tea are usually fine. Milk, sugar and juice break the fast.
Which fasting plan is best for beginners?
Many start with 14:10 or 12:12 and move to 16:8 once it feels easy.
What is the 5:2 diet?
Normal eating on five days and about 500 to 600 kcal on two non-consecutive days. It limits calories rather than hours.
Who should not fast?
People who are pregnant, breastfeeding, under 18, diabetic on medication or with a history of eating disorders should talk to a doctor first.