Intermittent Fasting Window Calculator
Eating and fasting window from your schedule.
Enter your values
ⓘ Live results
Results
- Eating window
- 12:00 - 20:00
- Eating window length
- 8 hours
- Fasting window length
- 16 hours
Quick answer
Your eating window starts at your first meal and lasts for the number of hours defined by your chosen fasting protocol.
eating window = 24 - fasting hours
How to use the Intermittent Fasting Window Calculator
- 1Choose your fasting protocol and enter the time of your first meal.
- 2The eating window is calculated as 24 hours minus the fasting duration.
- 3Intermittent fasting isn't suitable for everyone — check with a doctor if pregnant, breastfeeding, or managing diabetes or an eating disorder.
Worked example
Using the values the calculator loads with:
Inputs
- Protocol16:8
- First meal time (HH:MM, 24h)12:00
Results
- Eating window12:00 - 20:00
- Eating window length8 hours
- Fasting window length16 hours
Frequently asked questions
Which protocol is best?
There's no single best option — 16:8 is the most commonly sustained by beginners.
Can I drink water while fasting?
Yes, water, black coffee and plain tea are typically allowed and don't break a fast for most protocols.
About this calculator
- Built and reviewed by James Whitfield · How we build and test calculators
- Report an error
Results are estimates for general information. For medical, legal, structural or financial decisions, confirm with a qualified professional.