Most cardholders across America will see higher credit card interest rates within the next several weeks thanks to today’s Federal Reserve action which will likely boost the prime rate to 4.25%. Four of the nation’s top ten issuers use the last business day of the month, and one issuer uses the first day of the month, to determine rates for the next billing period, potentially affecting up to 180 million cardholders or 28% of the U.S. market by the end of July. The nation’s largest issuer, Citibank, sets its rates two days prior to the closing date of the billing cycle, providing an immediate impact to its 100+ million cardholders. Bank One and Providian use the 22nd day of the month to set rates, which will delay rate increases on their cardholders until August. However, Bank One is changing its index date, effective August 1st, from the 22nd day of the month to two days prior to the closing date of the billing cycle. MBNA and Capital One adjust rates quarterly, however both issuers predominately use fixed interest rates for their card products. Chase, Discover, Bank of America, and Household Bank use the last business day of the month as rate adjusting dates. American Express uses the higher of the 1st or the 20th of each month. The nation’s top ten credit card issuers have 493 million cardholders or about 77% of the total bank credit cards in the USA.