Intermittent Fasting Calculator
Pick a fasting plan and the time of your first meal to see your eating window, when to stop eating, and your fasting hours each week.
Eating window
12:00 pm to 8:00 pm
- Stop eating by
- 8:00 pm
- Fast
- 8:00 pm to 12:00 pm the next day, 16 hours
- Hours fasting a week
- 112 hours
Eat between 12:00 pm and 8:00 pm, then fast for 16 hours until 12:00 pm the next day.
How it's worked out
- Eating window
24 − 16 hours fasting8 hours - Last meal
12:00 pm + 8 hours8:00 pm - Fasting each week
16 hours × 7 days112 hours
Your day
| Time | What |
|---|---|
| 12:00 pm | First meal: the fast ends |
| 8:00 pm | Finish eating: the fast starts |
| 12:00 pm | Next day's first meal |
- Water, plain tea and black coffee are usually fine during the fast.
- Long fasts aren't suitable for everyone, including children, people who are pregnant or breastfeeding, and people with diabetes or a history of eating disorders. Check with a doctor first.
How it is worked out
The eating window is 24 hours minus the fasting hours, starting from your first meal. Your last meal is the first meal time plus the window, and the fast runs from then until your first meal the next day.
Questions people ask
What is my eating window on 16:8 if I eat at noon?
From 12:00 pm to 8:00 pm. You then fast from 8 pm until noon the next day.
What can I drink while fasting?
Water, plain tea and black coffee are usually allowed, as they have almost no calories.
Which plan should I start with?
Many people start with 12:12 or 14:10 and move to 16:8 once that feels easy.
Who shouldn't fast?
Children, people who are pregnant or breastfeeding, and people with diabetes, a history of eating disorders or other health conditions should talk to a doctor first.
About this calculator
Formula and rules last checked 10 November 2026Written and tested by the CalculatorDex teamReport a problem