There are nearly 21 million cost-burdened renters, according to a recent study by the Harvard Joint Center for Housing Studies.  A generally accepted definition of cost-burdened is spending more than 30% of your income on housing.  More than half of these paid more than 50% of income on housing.  In another study, by the National Low Income Housing Coalition, only 35% of extremely low income renters have an affordable unit available to them.