What changes when you let a till abroad bill you in won

Terminals and receipts abroad sometimes show a won figure and ask whether you would like to be charged in won. Accept, and the amount is fixed using a rate chosen on the merchant side with an added margin.

The confusion starts here. It feels as though the conversion is finished and no more fees can apply, but that fixed won amount still travels through the international network to your issuer. The card network fee and the issuer overseas service fee apply exactly as before.

Put the two formulas side by side and the difference is plain. Paying in local currency multiplies the amount by the network fee, the rate and the issuer fee. Being billed in won puts the added rate in front of all of that. Because it multiplies, a larger purchase widens the gap in proportion.

The calculator shows both lines together. Put an estimate in the added rate field and it shows what one payment costs either way, and what a year of the same payment comes to.

The added rate is set by the merchant or the terminal operator, so it can differ between two shops in the same country. That is why we cannot fill it in for you, and why an estimate from the two figures on your own receipt is the closest you will get.

A won figure on the screen looks like a final number, but it was built with a rate the merchant side chose. Pay in local currency and that step is replaced by your issuer's settlement rate instead. Which one wins depends on the rate that day and on the added rate, so the calculator puts the two lines side by side and leaves the choice to you.