The S&P CoreLogic Case-Shiller national home price index came out Tuesday morning, showing that prices in March were up 20.6% year over year. You read that right: 20.6%. Tampa, Florida, knocked Phoenix out of the top spot for price jumps with a 35% increase. 

Sure, Case-Shiller is a lagging indicator, and there are signs the run-up in mortgage rates we’ve seen over the past couple of months is cooling demand, just like Federal Reserve Chair Jay Powell wants.

But there’s a key factor keeping prices high: Very few people are putting their houses up for sale.

Back in early 2020, Becky Repka was ready to downsize. Her four-bed, two-bath home in Sacramento, California, felt too big for just her and her teenage son.

“I was just about ready to list it,” she said. “We’d gotten, honestly, everything cleared out and cleaned up and the photos taken.”

Then, COVID hit and Repka hit the pause button. Now, her home is worth over $100,000 more than it was two years ago. But so are many of the smaller places she would move into.

So, for now, she’s staying put. “And honestly even considering what my other options might be. Do I build out a mother-in-law unit I could rent out?”

On a typical day in April 2019, there were about 1.2 million homes up for sale. Last month, that number was 409,000. 

There’s a chicken-and-egg problem, said economist Danielle Hale with Realtor.com. Would-be home sellers don’t want to be would-be homebuyers right now. 

“So when the market is ultracompetitive, that is impacting their calculation on whether it’s a good time to sell,” she said.  

And since refinancing your home at record-low interest rates was as much of a pandemic pastime as baking your own sourdough, “that raises the cost for them if they’re thinking about moving, not just because of higher prices but because they’re also likely to see a higher mortgage rate,” Hale said.

There are other factors: Institutional investors with single-family rentals may be less likely to sell. But Zillow economist Nicole Bachaud said the main problem behind the lack of inventory is one you’ve probably heard before.

“If you go back to the end of the Great Recession, homebuilders stopped building at the level they did previously and didn’t pick back up until 2021,” she said.

It’ll take a while, Bachaud added, to build ourselves out of the shortage we’re in now.