Eligibility for the flexible-payment plans, and the details of your offer, vary with your history of managing credit and paying on time.

American Express introduced a flexible Pay It Plan It program for its consumer credit cards in 2017. The Plan It option allows cardholders to pay off large purchases over several months for a fixed monthly fee, rather than accruing double-digit interest by carrying over the purchase in their card balance.

Typically, customers use the planning option for amounts of around $650, and most often for travel and retail purchases — “think vacation flights or designer handbags,” the company said in an email. (The new program isn’t available on the company’s charge cards, which already offered “pay over time” plans, at a traditional interest rate.)

Users select one or more transactions on their digital statement, and are then shown options to pay the item off over time; terms can range from three to 24 months. The fee is disclosed upfront, and the payment is added to the account’s minimum monthly payment. The fee is up to 1.23 percent of the amount put into an installment plan, according to Amex’s card agreements.

Amex said the cost of the plan fee would always be the “same or better” than the cost of interest accrued for the same charge without a payment plan.

The company said it had seen “strong momentum” for the installment option, driven by millennials, generally people in their early 20s to mid-30s, who are three times more likely than customers in other age groups to use the feature.

Citibank recently began offering flexible payment options to “select” card customers in the United States. Citi’s offering works a bit differently: Cardholders can choose to pay off purchases monthly at a fixed interest rate, or they can take out a “flex loan” against the card’s existing credit line, also at a fixed interest rate. The rate on the flexible plans is not higher than the standard interest rate for purchases on the card, Citi said. The minimum amount to borrow is $500, while the maximum depends on the credit limit on the customer’s card.