London - It is the time of year when festive spending can quickly spiral out of control.
And experts warn this could lead to "financial infidelity" – couples hiding their spending and debts from each other.
More than a third of people in relationships are lying about their finances, a study has found. This can range from buying an expensive daily latte when they are supposed to be saving for a holiday, to hiding credit card bills or squirrelling away money in a secret savings account.
Researchers from four universities, including University College London, looked at a survey of more than 12 000 bank customers across 13 countries, including the UK.
They found almost 36 percent were engaging in at least one type of "financial infidelity" – managing money in a way their partner might disapprove of, and hiding the evidence.
A series of studies found men and women are equally likely to lie about money, regardless of wealth, with those least satisfied in their relationship most likely to do so.
Financial infidelity, which can also involve lending someone money without telling a partner, or hiding how much you earn, is said to be as "harmful" for relationships as cheating. Among more than 300 married couples, those especially likely to lie about money later reported feeling worse about themselves and less committed to their partner in questionnaires.
Dr Joe Gladstone, study co-author from UCL, said: "The findings indicate that financial infidelity is surprisingly common, and can be influential in terms of both relationship quality and in changing how people spend their money."
Dr Jenny Olson, of Indiana University, said: "Financial infidelity is probably rampant this time of year.
"You see the packages piling up, which makes you wonder how many people are purchasing things without telling their partners, or sneaking something they want on to the Christmas shopping list, hoping it won’t be noticed. The problem comes when the credit card bill arrives and potentially gets found out."
The study, published in the Journal of Consumer Research, gave participants a series of tempting financial scenarios likely to upset their partner and recorded whether they would give in and how they would try to hide it.
They concluded: "Financial infidelity has the potential to be as harmful for relationship health and longevity as sexual infidelity, as conflicts over money are also a primary reason for divorce."