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At a time when you can pay bills online and deposit checks remotely using a cell phone, it’s amazing how many Americans don’t have bank accounts. One in nine households is without a checking account.

And almost one-third of the population is underbanked — lacking the full range of basic financial services. Going without such services is not only inconvenient but also expensive. Someone who cashes paychecks or benefit checks at a check-cashing service and pays bills with money orders may end up spending more than $500 a year for transactions that would cost no more than $120 at banks that offer basic checking accounts.

“Life is more expensive for people who have less,” says Brian Blake, vice president of CheckSpring Bank, an institution in New York City’s South Bronx that provides banking services to low-income customers. The bank, which is changing its name to Spring Bank, is about to open a second branch in Harlem. “Even in gentrifying neighborhoods, there are lots of people earning less than $15,000 a year,” says Blake.

Not surprisingly, low-income people are the ones most likely to be underbanked, according to FDIC data. Among households with annual incomes of less than $15,000 a year, 28% have no bank account and another 22% have less than a full range of services. Rates of underbanking are similarly high among the unemployed, people without high school degrees and those under the age of 25. In addition, African Americans, Native Americans and Hispanics have higher rates than whites and Asians. Only about 5% of employed middle-class Americans are without bank accounts, but more than 20% use financial services outside the banking system — typically for reasons of convenience.

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It’s one thing, of course, for relatively affluent people to pay a fee to cash a check because they are in a rush, and quite another for someone to rely on so-called alternative financial services for all of his or her transactions. Check-cashing services in New York are permitted to charge 1.91%. If someone with a $15,000 income uses them regularly to cash paychecks, that could cost up to $286 a year. Postal money orders cost $1.15 apiece, so someone using them to pay three bills a month would spend another $41 a year. Other charges — for prepaid debit cards, say — could push the total cost to more than $500 a year. And the cost of consumer borrowing outside the banking system is horrific. A 30-day auto-title loan charges interest equivalent to an annual rate of 50% to 100% or more.

Why would people be willing to incur significant costs when a basic checking account and debit card can be had for $10 a month? Moreover, it’s possible to find accounts that are free if you can maintain a minimum level of savings, make a certain number of transactions a month or arrange to be paid by direct deposit. In addition, there’s a hidden cost to doing without bank accounts: you don’t establish a banking record. Basically, people forgo these opportunities for four reasons:

Services aren’t always available. Banks typically want to attract customers who will eventually want services that are more profitable. As a result, some institutions don’t offer products for customers with limited resources. In some states, banks are required to offer a low-cost basic banking service. But they have no reason to promote it and typically encourage new customers to choose a more expensive package of services. In addition, banks may not maintain many branches in areas with lots of low-income customers.

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People don’t have enough time or money. Workers who have long hours or a long commute to work may not be able to get to a branch during banking hours. If they are living paycheck to paycheck, they may not be able to wait for checks to clear. In such situations, getting immediate cash at a check-cashing service may be unavoidable.

Some people don’t trust banks. Recent immigrants may doubt the safety of banks. And many low-income people who could afford a basic account but would have a minimal balance worry that they might incur charges of $25 or more if they accidentally bounce a check or make some other error. In addition, although the use of direct deposit for paychecks makes money available more quickly and typically reduces monthly fees, some people may distrust electronic banking and prefer paper checks — or their employers may not offer direct deposit.

Potential customers lack financial literacy. The most difficult cause to quantify is whether people go outside the banking system because they don’t really understand how consumer finances work or how much nonbank alternatives charge. Each individual transaction costs relatively little, even though cumulatively they can add up to many times what a basic checking account would cost.

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While these problems are most severe for low-income people, all consumers face them in one way or another. Paying an extra annual fee for a card that give you airline miles, for example, is a waste if you don’t use the card enough over the course of the year. Choosing a banking plan that requires a higher minimum balance than you can easily maintain can lead to higher monthly fees. And incurring an unnecessary ATM fee because your own bank branch is too far away and you forgot to get cash earlier isn’t really any different from using a local check-cashing service.