The U.S. housing market needs nearly 4 million single-family homes to meet the nation’s demand, according to a new analysis from Freddie Mac. The 3.8 million shortfall marks a 52% increase in the housing shortage since 2018.

“This is what you get when you underbuild for 10 years,” says Sam Khater, Freddie Mac’s chief economist. “We should have almost four million more housing units if we had kept up with demand the last few years.”

Lawrence Yun, chief economist of the National Association of REALTORS®, has been among real estate economists leading the calls over the last few years for greater inventory and more homebuilding to meet demand. “We need to build more homes,” Yun told NPR, adding that since the housing crisis more than a decade ago, homebuilders have been building too few homes.

The housing shortage mixed with strong buyer demand since the pandemic is prompting home prices to rise rapidly. The median existing-home price for all housing types in February was $313,000, up 15.8% compared to a year earlier, according to the National Association of REALTORS®.

The housing shortage is most prominent among entry-level homes, and it’s making it more expensive for first-time buyers to enter the market, Khater told The Wall Street Journal.

Freddie Mac calculated the housing shortage of nearly 4 million by factoring in the amount of single-family homebuilding that would be needed to match the demand from household formation, second-home purchases, and replacement of damaged or aging homes. Researchers then compared it to the pace of construction in trying to meet that demand.

The nation’s homebuilders decreased their building during the 2007-2009 recession and kept construction levels lower in the years following. Builders have been ramping up construction, but they are facing many challenges, such as labor and lot shortages and the rapidly rising costs of materials, notably lumber.

Homebuilders need to construct between 1.1 million and 1.2 million single-family homes a year to meet long-term demand. That rate, however, would need to be even higher to remove the existing deficit, Robert Dietz, chief economist at the National Association of Home Builders, told The Wall Street Journal.