Should I choose with conversion or without conversion at a Thai ATM?

The screen is designed to sound helpful. It offers to show the amount in euros, pounds or dollars so you know what you are spending, and it often puts that option on the large highlighted button. The helpfulness is the product.

What dynamic currency conversion actually is

When you accept conversion, the ATM operator becomes your currency exchange. It picks the rate, sets the margin and bills the withdrawal in your home currency before it reaches your bank. ThailandKnowledge puts that margin at roughly 3 to 7 percent. When you decline, the withdrawal reaches your own card issuer in baht, and your issuer converts it at its own rate, which is the rate you chose the card for.

The arithmetic on one withdrawal

Take 20,000 THB. The machine fee at most Thai bank ATMs is about 220 THB, or 1.1 percent. Accept conversion at a 3 to 7 percent markup and the same withdrawal costs another 600 to 1,400 THB. One press of the wrong button can cost several times the fee you were already annoyed about.

What to press

1. Insert the card and choose the amount in Thai baht.
2. When the fee warning appears, accept it. That is the machine fee, and there is no way round it at that ATM.
3. When the conversion screen appears, choose without conversion, continue without conversion, or decline, depending on the wording.
4. If the machine cancels the withdrawal because you declined, try another bank's ATM rather than accepting the rate.

The same trap in shops and restaurants

Card terminals in tourist areas offer the identical choice, phrased as paying in your home currency. Choose baht every time, and if the staff member has already pressed it for you, ask for the payment to be cancelled and run again. On Koh Tao, the Koh Tao Complete Guide notes that resorts, dive schools, restaurants and supermarkets often add 3 or 4 percent for card payments, which is a separate charge on top.

The fee itself, why some screens now show 250 THB or more, and the cheapest machines are in our post on the real cost of cash in Thailand. Compare what your card should give you with Currency Check, and see the full money picture in our Thai bank account and money guide.