Credit Cards Cost, No Matter What

· Paying with cash is a visual clue that money is being spent. And while checks don't have the same effect, writing down the amount physically still imprints on your brain that you are letting go of some cash.

If you don't believe the research, try this experiment: For one month, don't use a credit card. Make all your purchases with cash. After the month is over, compare your spending with the previous month when you used credit.

If it's true that you don't transact more when you use plastic, your spending behavior during the experimental month should be exactly the same.

Without fail, when I have people do this experiment, they realize they, in fact, are buying more on plastic, even the folks who are capable of handling and paying off their purchases during the billing cycle.

I haven't given up on using credit -- yet. But I'm mindful that I do spend more when I swipe that card. Like others who use credit cards for the convenience, I may not be weighed down by this debt, but to say that there is no extra cost vs. cash is irrational.

· On the air: Michelle Singletary discusses personal finance Tuesdays on NPR's "Day to Day" program and online athttp://www.npr.org.

· By mail: Readers can write to her at The Washington Post, 1150 15th St. NW, Washington, D.C. 20071.

· By e-mail:singletarym@washpost.com.

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