Yes, taking your credit card on vacation can pose a real risk, but not for the reasons you may think. I’m not suggesting you leave it behind so you can resist the temptation to splurge on a scuba lesson you hadn’t budgeted in, or from buying that pair of Manolo Blahnik knockoffs you really, really hadn’t planned on getting – although if you’re prone to spontaneous spending that might not be a bad idea.

I’m talking about avoiding a fee that most card companies don’t advertise they charge you, but which can add a whopping three per cent to your purchase abroad: foreign transaction fees.

If you travel and buy something outside the country with your credit card, you can be charged up to three per cent of your purchase for the card issuer and the institution (Visa, Mastercard) to do the conversion from other monetary units to US dollars. Not only that, but they will charge you even if you’re buying online from a business located outside the United States.

The reason for the charge is, ostensibly, to protect you from fraudulent companies. The credit card company will usually underwrite the risk if it turns out you bought from a bogus business. But some argue that three per cent is pretty high to justify either the “cost” of calculating the foreign currency to dollars, or for bearing the cost of fraudulent transactions. How exactly credit card companies started levying this fee is a bit of a convoluted story, but where we’re at now is that you won’t know you’re being charged for an out-of-country purchase until you get the bill, or you already know about the system.

Or, if you’re a smart consumer and have one of two credit cards who don’t charge fees for foreign transactions: a credit card from Capital One or from Schwab Bank. Both of these institutions, as well as some cards issued by smaller banks or credit unions, have made the decision to charge nothing for the privilege, according to a NYTimes business article (Feb 20). Even though Visa and Mastercard still charge Capital One a fee for converting the transaction, they have chosen to waive the fee in order to attract customers.

So if you travel a lot or buy a lot online from overseas, you’d be wise to check your bill to see whether an additional charge has been tacked on. If there is, and if you don’t want to keep paying it, then my advice is to tuck your card away, or sign up for one that doesn’t gouge. There are still a few good cards out there.