You set up a spreadsheet that analyzes your beer consumption rate per day, how much kegged/bottled brew you have on hand, how much are in fermenters, and the date you will have no beer. The calculations determine the last possible date you need to brew more, taking into account fermenting days, secondary fermenting days, dry hop days, and carbonation days so you don't run out of beer. And just to be extra cautious, figure the next 2 brew dates as well. After all, when it comes to home brew, it's better to have too much than enough.