Lending Club, a “peer-to-peer” platform matching borrowers and lenders, is expected to float its shares today, having raised $870m at a valuation in excess of $5.4 billion. Founded in 2007 and based in San Francisco, it is the biggest of a bunch of startups hoping to usurp conventional bank loans and credit cards. The value of loans facilitated by Lending Club has roughly doubled every year; more than $1 billion was shifted in the latest quarter. That’s impressive, but still small next to American consumers’ total debts of $3 trillion. To justify its punchy valuation—there are no profits to speak of—investors must believe it can keep growing fast. More important, Lending Club has to prove its snazzy algorithms are indeed better than banks at identifying who is creditworthy and who is not. Though it has lower costs than banking rivals, that is meaningless if its borrowers all default come the next recession.