Intermittent Fasting Calculator
Fasting Method
12:00 PM
Eating Window12:00 PM - 8:00 PM
Fasting Hours16 h
Eating Hours8 h
Fast from 8:00 PM until 12:00 PM the next day, then eat all meals within the 8-hour window.
The Intermittent Fasting Calculator turns a fasting method and a chosen first-meal time into a clear daily timetable. Pick a popular protocol such as 16:8, 18:6, 20:4, or OMAD, and the tool works out exactly when your eating window opens and closes and how long you fast in between. It is a scheduling aid that takes the mental arithmetic out of timing your meals.
How it works
- Select a fasting method, which fixes the split between fasting hours and eating hours (16:8 means 16 hours fasting and 8 hours eating).
- Set the time of your first meal of the day using the slider.
- The calculator adds the eating-window length to that start time to find when the window closes, then treats the rest of the 24 hours as your fast.
Worked example
Following 16:8 with the first meal at 12:00 PM.
- 16:8 means an 8-hour eating window and a 16-hour fast.
- Eating window opens at 12:00 PM.
- Add 8 hours: the window closes at 8:00 PM, and you fast from 8:00 PM until noon the next day.
Eat between 12:00 PM and 8:00 PM, fast the other 16 hours.
Frequently asked questions
- What does OMAD mean?
- OMAD stands for One Meal A Day. It is an aggressive schedule with roughly a 23-hour fast and a single one-hour eating window, so all daily calories are consumed in one sitting.
- Can I drink anything during the fasting window?
- Water, black coffee, and plain tea are generally considered fine during a fast because they contain essentially no calories. Anything with sugar, milk, or sweeteners may break the fast for some goals.
- Which fasting method should a beginner choose?
- Most people start with 16:8 because the 16-hour fast largely overlaps with sleep and is easy to sustain. Longer fasts like 20:4 or OMAD are usually adopted gradually after building the habit.