The 12 US cities with the fastest-rising rent prices

If you've hunted for an apartment in a US city in the past several years, you might have noticed that it's getting more and more difficult.

In the past decade, nine million Americans have become new renters, many of them in cities. Yet the average renter can afford less than 40% of the available apartments in the country's 11 largest metro areas, according to a 2016 New York University analysis.

Every year, Zillow generates a median rent index at seven geographic levels including neighborhood, zip code, city, congressional district, county, metropolitan area, state, and the country overall. Nationwide, the median rent has increased by 2.2% compared to 2015. At the city level, Zillow considers rent markets for studios, condos, single-family homes, and one to five bedroom apartments.

Here the 12 cities with the biggest change from last year.