Brits spend £17 billion more on cards each month than they think, according to a survey by Egg.
The survey found that UK consumers are naïve when it comes to their spending habits - most believe they spend £236 billion on their trusty plastic when in fact the real figure is £437 billion a year.
A spokesperson for Egg said: "Plastic is clearly the choice of the UK consumer when it comes to spending, but our Egg Money research clearly indicates that the increasingly complex nature of our finances means it is often hard to keep track of how much we are spending."
According to the study, the average British consumer spends £775 a month on credit cards and debit cards, but when surveyed, people thought that they only spent £418 a month.
Over half of people admitted that they were unsure of how much they had actually spent.
Of the consumers polled, one in three said that separating their spending money from money for bills and necessities would help them control their spending.
Egg Money is Egg's latest account which offers customers the chance to separate their finances to help them manage their money more effectively.
According to the British Bankers Association, credit card holders paid off more debts in August than previous months.
They also reined in spending and managed to spend less on plastic in for the second time this year in August.To read more about Savings Accounts, click here.
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