The researchers compared all twenty-six different study schedules, and calculated the best intervals given different test dates. “To put it simply, if you want to know the optimal distribution of your study time, you need to decide how long you wish to remember something,” Wiseheart and Pashler’s group wrote. The optimal interval ranges can be read off a simple chart: Have a close look. These numbers aren’t exact; there’s wiggle room on either side. But they’re close.