Originally Posted by littleleaguemom
Whatever Amex says they do, I've found the charge on my statement is about 3% more than the interbank rate for the day and 1% more than Diners Club and 2% more than MBNA, both before the latest switcheroo.
Based on my calculation AMEX charges 2.5%-3% more than interbank rate. But since AMEX does not disclose which date is used to calculate the conversion, I have not been able to figure out the exact markup. I did notice that for countries that peg their currency to US$, AMEX's conversion rate could still vary by .25%, based on the date of the transaction.
AMEX may not be the one with the most markup nowadays, but they certainly are the worst in terms of disclosure.