(Correction: A previous version of this report used incomplete inventory data in four cities – Charlotte, Modesto, Sacramento and Stockton. Redfin removed those cities while it corrects the data. With 46 instead of 50 markets included in the analysis, the overall share of stale inventory rose from 70.2% to 70.9%.)

As the spring selling season gets into full swing, Redfin examined 46 markets to see if fresh inventory is growing, and whether it’s growing enough.

As of March 31, nearly 71% of homes on the market were stale, meaning they had languished unsold for more than a month, according to the latest report by real estate brokerage Redfin.

New listings shot up 9.2% last month, but the spring housing bounce is so far nowhere near big enough to satisfy demand.

Nationwide, the total number of unsold homes rose 5.3% in March to 2 million, but at the current pace of sales, that supply would be exhausted in only 4.6 months, according to the National Association of Realtors.

In the 50 markets Redfin analyzed, about 30% of unsold houses were fresh as of March 31, up from about 24% three years ago.

In Charlotte, where the number of properties for sale is at its lowest in at least three years, fresh listings — those less than 30 days old — accounted for only 5.5% of Charlotte’s inventory as of March 31, also a low. Last month, only 55 new properties came on the market, compared with 225 a year ago.

Redfin asks what’s causing the inventory crunch and what they found is that, according to RealtyTrac, more than 7 million homeowners can’t sell because they’re deeply underwater, meaning they owe more on their properties than they’re worth. That figure is falling as rising home values put more homeowners into the black, but those same price gains, coupled with weak wage growth and tight credit, are discouraging many from selling and trading up. Builders haven’t kept pace, either.

They’re breaking ground on 1.07 million houses, condominiums and apartments a year, but the U.S. requires between 1.6 million and 1.9 million new units just to accommodate population growth and household formation, according to the Harvard Joint Center for Housing.

In Indianapolis, even a 26.6% year-over-year surge in new listings in March wasn’t enough to replenish depleted inventory. Inventory is so low in Oakland, Denver and Dallas-Fort Worth that fresh listings abnormally accounted for a larger share of inventory last month as buyers whittled away at less-desirable properties and builders raced to keep up with demand.

Dallas-Fort Worth added more than 100,000 people between 2013 and 2014. Last month, there were 14,332 fewer properties for sale than in March 2012. New listings fell more than 27%.

“All the desirable properties are getting snatched up in three days. The ones that are left become our stale inventory,” Dallas Redfin agent Connie Durnal said. “It’s driving the prices up and increasing multiple offers. I don’t see it ending.”