DCC is not possible with Amex.
Visa and Mastercard publish their exchange rates in advance, so it is always possible to know exactly what you will be charged to the cent (provided you have internet access at the right time and you know what your bank's fee will be).
The Visa exchange rate is updated at midnight UTC, currently 11am Sydney time.
The Mastercard exchange rate is updated at 3.05pm Eastern Time (US), currently 7.05am Sydney time.
(Mastercard used to only publish its exchange rate a day or two late, but this changed in August 2020.)
All my foreign transactions with cards issued by banks in 3 different countries have always used the exact rates quoted by the websites I linked above at the time of the transaction (there seems to be several minutes of leeway with the Mastercard one if you are doing the transaction around 3pm ET).
I believe the HSBC Aus debit card (the one which gives 2% cashback for contactless txns inside Aus) is an exception for certain currencies, where it uses HSBC's own exchange rates.
Visa and Mastercard publish their exchange rates in advance, so it is always possible to know exactly what you will be charged to the cent (provided you have internet access at the right time and you know what your bank's fee will be).
Currency Converter – Exchange Rate Calculator
Exchange Rates & Currency Conversion Calculator – Use the converter to get an indication of the rate you may receive when using your Visa card. Learn more.
www.visa.com.au
Mastercard Currency Converter | Currency Exchange Rate Calculator
Mastercard currency converter tool calculates foreign exchange rates for all the major currencies worldwide to enable cross-border purchases and ATM transactions.
www.mastercard.com
The Visa exchange rate is updated at midnight UTC, currently 11am Sydney time.
The Mastercard exchange rate is updated at 3.05pm Eastern Time (US), currently 7.05am Sydney time.
(Mastercard used to only publish its exchange rate a day or two late, but this changed in August 2020.)
All my foreign transactions with cards issued by banks in 3 different countries have always used the exact rates quoted by the websites I linked above at the time of the transaction (there seems to be several minutes of leeway with the Mastercard one if you are doing the transaction around 3pm ET).
I believe the HSBC Aus debit card (the one which gives 2% cashback for contactless txns inside Aus) is an exception for certain currencies, where it uses HSBC's own exchange rates.