How do you do intermittent fasting? A lot of IF'ers eat for 8 hours a day, not eating the various other 16 hrs. The length of time do you need to fast for intermittent fasting? You can start with a 12-hour quick as well as function your means to 16 hrs. Most IFer's eat from 10-6, 11-7, or 12-8. It doesn't matter what eating window you pick, equally