THE ADVANTAGES TO

automatic bill pay are obvious: No 41-cent stamps to buy, no payment schedules to juggle, no late fees to worry about.

Over the past five years, a whopping 56% of Americans arranged to have at least one regular bill paid automatically, according to market research firm eMarketer. But just because you're not sitting down to write out checks each month doesn't mean you don't have to pay attention. "Automatic doesn't mean autopilot," says Curtis Arnold, founder of CardRatings.com. "You can't just set these payments up and let them cruise."

There are plenty of things that can go wrong, whether you're setting up regular payments through your credit card or financial institution, or allowing a company you owe to dip into your accounts. Watch out for these six automatic payment pitfalls:

1. Late Payments

Just because you set up automatic payments for, say, the first of the month, don't assume that your payment will be received at your lender by the next day even if the payment is made electronically. "Nothing is really instant not even automatic online bill pay," says Edgar Dworsky, founder of

. "Many automatic payments are sent by good-old-fashioned check." (That's why online-bill-pay systems ask for the company's mailing address, as well as your account number.) The difference in processing time between a true electronic payment and a check can be as many as five days.

Solution: How a payment is sent depends on your financial institution or credit-card issuer, and the relationship it has with your payee. Ask your bank whether cash will be sent electronically or via check, and plan accordingly. Because many credit-card issuers and other companies have set tighter deadlines that include time as well as date, pad an extra day onto your automatic payments to ensure it arrives on time.

2. Lost Payments

Automatically sent doesn't always translate to automatically received. There's plenty that can go wrong between Point A (you) and Point B (the payee). "Sometimes they just don't get the payment," says Linda Sherry, a spokeswoman for Consumer Action. Sometimes the financial institution mishandles sending out the money. Other times, the check does indeed get lost in the mail. Or the payee may not have processed it correctly. Another common ding: change of address. "Credit cards are notorious for changing the address to which you send payment," says Dworsky.

Solution: Arrange confirmation through your bank and bill-payees. Verizon Wireless, for example, lets consumers sign up for email or text message notification when payment has been received. You can also get a warning message if you miss a due date. Bank of America assigns codes to bill-pay transactions that the recipient has cashed or processed.

3. Unexpected Withdrawals

When you set up automatic payments through a company with which you do business, you have little control over just when they pull money from your account and with a fluctuating bill, even how much they take, says Scott Bilker, founder of

. "Say you pay your cellphone bill automatically," he suggests, "and your teen racks up a $1,000 text-messaging bill. When you're thinking you're on the $30-a-month plan and it is actually $1,030 coming out of your checking account, that's not fun. And it's harder to dispute, because they've already taken that money."

Solution: Consider skipping auto-pay for bills that fluctuate month to month, says Bilker. "Sending them individually gives you another chance to look over your account and make sure everything is right," he says.

4. Incorrect Withdrawals

Computers make errors. Those that handle automatic payment and online-bill-pay systems are no exception. There are plenty of ways auto-pay can go wrong from double billing to a single charge that's bigger or smaller than it should be.

Solution: Keep tabs on your transactions, especially if the bill pay in question is being withdrawn from your checking account. Consider scheduling payments through your bank, which offers you more control.

5. Difficult Cancellations

Automatic payments are the zombies of the finance world, says Sherry: They keep coming back long after service has expired, and are difficult to stop. Internet service providers and fitness clubs are particularly notorious for continuing to charge you long after you've cancelled service. "It can be hell to get them off your back, to get the payments stopped," she says.

Solution: Notify your bank or credit-card issuer of the problem. Either can issue a stop-payment notification and prevent a particular company from putting charges through again. "That doesn't stop the company from coming after you to collect," cautions Sherry. To make the problem go away entirely, you'll need to get the company to agree to stop billing you.

In the future, provide companies with your credit-card number, rather than debit card or checking account information. For disputed charges, credit cards offer better protection. "Technically, under federal law, you can't challenge a problem with a service or charge on your debit card," says Dworsky. "Visa and MasterCard do allow it, but you're not federally protected."

6. Bill-Pay Fees

As online bill pay becomes more popular, most financial institutions are offering it (including automatic bill pay) free of charge. There are, however, a few stragglers that make mailing handwritten checks and buying 41-cent stamps seem cheap in comparison. Chase charges a $4.95-per-month bill pay fee to consumers using its Basic Checking, Budget Checking and other select accounts, while Wells Fargo bills Basic Checking account holders $6.95 a month for up to 25 bill-pay transactions; 40 cents each thereafter.

Solution: Banks that charge are the exception, rather than the rule. Shop around for a financial institution that's friendlier to your balance with free automatic bill pay.