American Express Co. plans to debut an online loan platform for small-business clients this year, targeting territory occupied by startups like Square Inc. and On Deck Capital Inc.

AmEx’s venture, Working Capital Terms, will approve loans in minutes for existing small-business cardholders, who can use the money to pay vendors. Debts may range from $1,000 to $750,000 with fees of 0.5 percent for a 30-day loan to 1.5 percent for a 90-day loan. AmEx will deposit funds directly into vendors’ accounts in as soon as two days.

“We’ve combined the convenience of the online lender with the competitive pricing of a bank loan,” Susan Sobbott, AmEx’s president of global commercial payments, said in a telephone interview. “It’s a big opportunity for us to go into an area where businesses want to pay vendors that don’t accept any credit cards.”