“Decent, affordable housing is fundamental to the health and well-being of people and to the smooth functioning of economies. Yet around the world, in developing and advanced economies alike, cities are struggling to meet that need. If current trends in urbanization and income growth persist, by 2025 the number of urban households that live in substandard housing—or are so financially stretched by housing costs that they forego other essentials, such as healthcare—could grow to 440 million, from 330 million. This could mean that the global affordable housing gap would affect one in three urban dwellers, about 1.6 billion people. A new McKinsey Global Institute (MGI) report, A blueprint for addressing the global affordable housing challenge, defines the affordability gap as the difference between the cost of an acceptable standard housing unit (which varies by location) and what households can afford to pay using no more than 30 percent of income. The analysis draws on MGI’s Cityscope database of 2,400 metropolitan areas, as well as case studies from around the world. It finds that the affordable housing gap now stands at $650 billion a year and that the problem will only grow as urban populations expand: current trends suggest that there could be 106 million more low-income urban households by 2025, for example. To replace today’s inadequate housing and build the additional units needed by 2025 would require $9 trillion to $11 trillion in construction spending alone. With land, the total cost could be $16 trillion. Of this, we estimate that $1 trillion to $3 trillion may have to come from public funding.”