At a time when people are paying down their credit, some consumers are turning to their debit cards. When they overspend on their debit cards, banks make money from overdraft fees.

This year alone, banks are expected to bring in $27 billion by covering overdrafts on checking accounts, typically on debit card purchases or checks that exceed a customer’s balance.

When you hit your limit on a credit card, your charge may be denied. When you hit your limit on a debit card, you are hit with fees for spending more than is in your account.

To avoid fees, if you bank doesn’t enforce a minimum amount, create your own minimum, so instead of your actual balance at zero, consider your minimum balance as $200 or so, just enough to make some small purchases and won’t have to pay a fee.

Overdraft protection fees are great sources of income for banks. When ATMs and debit cards were first created, users who didn’t have enough money had their requests denied. Now since some cards are associated with Visa and MasterCard there is the option to charge something using the same card.

According to the F.D.I.C. study, a $27 overdraft fee that a customer repays in two weeks on a $20 debit purchase would incur an annual percentage rate of 3,520 percent. By contrast, penalty interest rates on credit cards generally run about 30 percent.

Thirty percent! No one would want to pay 30% for a charge, but overdraft fees may be as high as $35 for each charge.

Ideally, if you don’t have the money in the account, then a bank should not allow the transaction to go through. This isn’t what happens. Have a debit card? Find out about your bank’s overdraft policy. Ask whether or not you will be automatically charged if your balance falls below a certain amount. If so, then start using cash for small purchases if they are the ones that make you spend then don’t make any small purchases. Knowing that the overdraft fee annual percentage rate exceeds 3000% makes it more difficult to just use a debit card with reckless abandon. A credit card would be better in some instances, especially if you know you can pay the amount within a month.