Housing prices continued to rise in January, up more than 19% from the year before according to S&P CoreLogic Case-Shiller index. A variety of market forces are at play, supply of homes chief among them. Supply in the U.S. is just really, really low right now.

“If you pick a typical town or neighborhood, and let’s call the normal level of inventories 200 [homes for sale] and then last year, it fell to 50. And so everybody’s saying, ‘Wow, inventories really dropped.’ Now it’s eight, where there’s an utter collapse,” said Jonathan Miller, president and CEO of real estate appraiser Miller Samuel.

The National Association of Realtors says the total housing inventory in February nationwide was 870,000. According to Redfin chief economist Daryl Fairweather, its numbers show inventory is down 23% from last year. “It was an all-time low in the last four weeks,” Fairweather said, as people rushed to buy homes while mortgage rates were still low.

But now, interest rates are rising. Earlier this month, mortgage rates rose above 4% for the time since 2019. Fairweather says that should cool the housing market.

“And I think that’s actually a good thing,” she said.

National Association of Realtors chief economist Lawrence Yun said that wouldn’t solve the inventory problem: “It’s not going to fix itself in a short time, even with mortgage rates inching up.”

Between rising rates and rising prices, Yun said, buyers could end up paying 40% more for a mortgage on the same house today compared to a year ago.