It's gotten a lot harder to borrow money from the raft of fintech firms looking to bring online lending into the mainstream.

Besieged by a wave of defaults after several years of rapid growth, the biggest online lenders have been forced by bond investors to tighten underwriting standards. Social Finance, Prosper, LendingClub and Avant now demand higher average credit scores and offer shorter maturities to boost the quality of loans they repackage into asset-backed securities.

The shift in the $30 billion market comes after a swarm of borrower defaults in the past three years rattled ABS investors. It also marks a coming of age of sorts for the fintech startups that offered cut-rate loans to build a customer base. Now, with rates rising and a potential economic slowdown looming, the move toward higher-quality from the push for quantity has taken on added urgency.

"They all had a pretty tough time and took losses a lot more than expected," said Henry Song, a portfolio manager at Diamond Hill Capital Management Inc., a Columbus, Ohio-based investment firm that invests in online-lending securitizations and manages $23 billion. "Some dropped certain grades and the mentality of grabbing market share to be profitable has shifted."

Fintech startups have sprouted up in recent years to target younger borrowers who are more comfortable applying for loans online and who have been underserved by traditional banks. The group, which tends to specialize in student and personal loans for cash-strapped millennials, hasn't been without growing pains. Many lenders have high default rates even as unemployment levels fall to multidecade lows.

"Yields were going down, a lot of that was due to competition. They were lowering rates just to stay competitive with each other," Bill Kassul, a principal at Ranger Capital Group in Dallas, Texas, said in an interview, adding that his firm used to invest in online-lending ABS. "We stopped investing because the risk/return wasn't as high."

Online lenders have responded to higher default rates and increased write-offs by raising interest rates, rejecting consumers with lower credit scores and shifting toward shorter-term loans, according to Kroll Bond Rating Agency.

"We have seen many of the platforms tightening their underwriting or essentially eliminating certain segments," said Rosemary Kelley, a senior managing director at Kroll, in an interview. "They are changing certain criteria in order to move up-tier somewhat in terms of the credit that they're taking."

The number of ABS issued by online lenders that saw performance triggers activated by missed payments declined last year, even as total loan losses rose, Kroll said in a recent report. That signals an increase in overall quality in the securities.

For instance, San Francisco-based Prosper, the third largest online lender, said in its most recent earnings report that its loans in the first quarter were less risky compared to those issued in the same time frame last year.

According to Kroll, the weighted average of FICO credit scores of Prosper's loans packaged in ABS increased to 717 in a March 2018 deal from 704 in a sale two years earlier.

"Defaults in the general unsecured consumer credit market (which includes marketplace loans) have been on the rise," Prosper said in a emailed statement. "Prosper has been watching this trend and tightening credit since 2017, and we expect credit tightening to continue in 2018."

The second largest lender, SoFi, increased the weighted average of its FICO credit scores to 744 in a sale earlier this year from 732 in a deal at the start of last year. The company declined to comment.

Bonds sold last week showed the safer structures are paying off. Avant, the fourth-largest online lender, increased the size of its sale by about $60 million and saw spreads narrow to 70 basis points in its top shelf of debt from 80 basis points in a previous deal in April. That came after the firm cut the average duration of the loans to 36 months in a deal this month from 43 months two years ago.

LendingClub, the largest of the group though a relative newcomer to the ABS sector, has also responded by eliminating the riskiest borrowers in its loan offerings.

"Investors are changing their behavior on the margin and tending to gravitate toward higher quality, lower risk grades," Jessie Szymanski, chief of staff to LendingClub's capital officer, said in a phone interview.

The expansion of online lending has led directly to an expansion of securitization as companies become more dependent on it for revenue. The sector is expected to increase the amount of loans it turns into securities by 29 percent from a year earlier to $18 billion this year, according to New York-based research firm PeerIQ.

Some investors still aren't convinced.

Tracy Chen, a Philadelphia-based portfolio manager at Brandywine Global Investment Management, said her firm doesn't invest in marketplace lending because there is not enough data on the sector.

"This market hasn't gone through a credit crisis so it's hard to find conviction of how it will perform," Chen said.

Bloomberg News