ImageEveryone has bad habits. Maybe you obsessively check Facebook while at dinner with friends, arrive late to meetings or interrupt people when they’re talking. Chances are you’re at least sometimes aware of these bad acts. But you might not realize how other habits are costing you actual money. And we’re not talking about a daily Starbucks fix. If you get pleasure out of those lattes, by all means enjoy them.

But some other under-the-radar tendencies can end up sabotaging your financial health, and you may not even realize it.

1. You shop with friends

Shopaholics are typically portrayed by women in popular culture. But at least in one respect, men can out-shop women. A 2011 study, “The Influence of Friends on Consumer Spending,” found that men spend more when they’re accompanied by a friend than when they’re alone, and the effect wasn’t the same for women.

The results of four experiments showed that men shopping with a buddy spent 54% more than men shopping solo, while women spent about the same whether they shopped by themselves or not. The authors posit that the reason for the discrepancy comes from a key difference between men and women – albeit a gender stereotype. Men focus on status and “engage in self-promotion through increased spending while shopping with friends” – in other words, they tend to show off – whereas women are “communion-oriented,” meaning they aim for cooperation and harmony, “leading them to keep their spending under control in the presence of a friend.”

2. You fall for complicated cellphone contracts

You buy a new smartphone; it comes with a monthly usage fee based on data consumed, an early termination fee and a complicated two-year contract. The problem: Many people underestimate how much data they’ll use and end up exceeding their plan limit, while others overestimate their future usage and pay for minutes they never use. Oren Bar-Gill, a professor at New York University’s School of Law, studied pricing misperception in the cellphone market, and found that many consumers choose the wrong plan for their needs.

In a 2009 study, Bar-Gill, author of “Seduction by Contract: Law, Economics, and Psychology in Consumer Markets,” analyzed data on the plan choice of more than 3,500 cellphone users and their usage patterns (how many minutes they talked each month for 20 months). He calculated the total amount each paid for service given their chosen plan, as well as the amount they would’ve paid given their actual usage. Bar-Gill found that more than 65% of users signed up for plans that didn’t fit their specific usage patterns, and based on that data, estimated that consumers lose a total of $13.3 billion annually.

3. You’ve got a credit mindset

Studies going back to 2001 have shown that consumers spend more when using credit cards compared to buying with cash. Two MIT professors set out to determine if research participants would be willing to pay more for an item simply because they were paying for it with a credit card instead of cash. They set up an auction where participants could bid on tickets to a basketball game. The participants who were told they could pay with plastic submitted significantly higher bids – nearly twice as high as the average cash bid.

A 2008 study published in the Journal of Experimental Psychology found that the “more transparent the payment outflow, the greater the aversion to spending, or higher the ‘pain of paying.’” Basically, paying $600 for an iPad in cash hurts more than handing over your Visa. Cash is viewed as the most transparent form of payment; less-transparent payment modes, such as credit cards and gift cards, are more easily spent or treated as play or “monopoly money,” the researchers said.

4. You have multiple bank accounts

Conventional wisdom suggests people should spread their earnings across different accounts to maximize savings. But a recent study found that having more accounts has the opposite effect.

Researchers at the University of Utah and University of Kansas conducted studies that presented 566 participants with the opportunity to earn money across tasks and spend it on different products. The authors found a higher rate of saving among individuals who maintained one account compared with those who had multiple accounts.

The reason? People look for an excuse to spend, and “vague” information makes it easy to justify that spending. Having multiple accounts makes it seem like you’ve got more funds available than you actually do. Having a single account – and one number reflecting your total wealth – makes it harder for individuals to come up with creative justifications to spend.

5. You divide your money into buckets

People tend to separate their money into categories, often based on where the money came from and what its intended use is – this much is for the house, this much for the kids’ college tuition, this much for movies, etc. In behavioral finance parlance, this is called mental accounting – and can make us act irrationally.

For instance, you might have a savings account that earns a paltry 0.4% in interest while keeping a balance on a 14%-APR credit card. You keep the money sitting in the bank even though using it to pay off your balance could save in interest expenses – and ultimately, your total net worth would be the same.

Research conducted by Justine Hastings of Brown University and Jesse Shapiro of Chicago Booth School of Business found a similar effect when people buy gas. The authors analyzed data on purchases of gasoline from a large grocery chain from 2006 through 2009, and found that people bought cheaper, lower-grade gas as if they were poorer than they were. The authors were able to track the participants’ other purchases in the grocery store, and saw that, while consumers scaled back from premium to regular gasoline, they didn’t cut back on orange juice purchases. Consumers saw their budget for gas as distinct from other expenses, suggesting they’re inept at budgeting across spending areas.