Holidaymakers are being stung because they are not aware how much it costs to use their debit cards abroad.
Research from Norwich and Peterborough Building Society (N&P) shows that almost one in three Britons overspent on their last foreign holiday.
Much of the overspending is being caused because of a lack of knowledge of how withdrawing cash abroad can pile on the pounds.
Before travelling, people should ensure they know how much it costs to use their credit and debit cards abroad.
On average holidaymakers think they would be charged £4.20 in fees to withdraw £250 from an overseas ATM using their debit card, but in reality it can cost nearly three times that at a few pence short of £12.
One in ten people think that withdrawing money abroad is free.
Just one in 20 (6%) of those questioned accurately estimated that most providers are likely to charge them £10 or more in fees to withdraw £250 worth of local currency.
With 55 million trips abroad by UK residents in 2010, the potential unexpected cost to consumers could be astronomical.
Ewan Edwards, head of current accounts at N&P, said: "It might seem boring to stick to a budget when you are on holiday, but overspending can mean paying for your annual holiday for months to come.
"Keeping control of costs is important. Over the years people have realised the increase in cost of using a mobile phone abroad and have altered their behaviour to ensure they aren't stung by a massive phone bill when they return home.
"The same thinking should apply to the plastic you take on holiday with you."
Check out our latest travel tip "Don't be caught out by overseas card charges"
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