Low interest rates have prompted a record number of Americans to refinance their homes this spring. An online mortgage loan startup that has seen strong growth from the borrowing surge is now seeking new financing at a sharply higher valuation than at its last influx of cash a year ago.

Better.com is nearing a deal to raise more than $100 million in new funding that would value the company at about $4 billion, up from about $720 million last year, two people familiar with the matter said. The company has told investors it expects revenue to grow from about $100 million last year to more than $800 million this year, the people said.