citibank 的网站是这样说的:
8.88% p.a. (daily interest) - Cardholders who promptly settle their payments with >50% of their monthly outstanding balance for 12 consecutive months
15% p.a. (daily interest) - Cardholders who promptly settle their minimum payment due for 12 consecutive month
17% p.a. (daily interest) - Cardholders who promptly settle their minimum payment due for 10 months or more in a 12 month cycle; and
18% p.a. (daily interest) - Cardholders who do not fall within the above categories