The study published earlier this month by real-estate research firm Zillow examined how much a person would have to earn to afford rent in more than 15,000 cities around the country without spending more than 30 percent of their annual income. "There's a common rule of thumb that says annual housing costs should not exceed 30 percent of one's annual income," wrote the report's author, Cory Hopkins. Unfortunately for single renters making the federal minimum wage of $7.25 per hour, it's virtually impossible to find a property in the U.S.