The calculation formula of total interest for credit card installment repayment is: interest = installment amount * installment fee * installment number. Suppose the consumer spends 3000 yuan to apply for three-phase repayment, and the installment fee is 1%, so the total installment interest is 3000 * 1% * 3 = 90 yuan.

Usually, the more credit card installments, the more interest banks charge.