Three quarters of the world's poor, living on less than $2 a day, have no bank account, further driving the vicious cycle of poverty, the World Bank said in a report Thursday.
The lack of bank access stemmed not only from poverty itself, but also because of the cost, travel distance, and the paperwork involved in having a bank account, the report said.
"Those without access to formal banking often have to rely on money lenders who often charge high fees. The 'unbanked' are also less likely to start their own business or insure themselves against unexpected events," it said.
According to the bank, 2.5 billion people are without access to formal banking.
World Bank president Robert Zoellick highlighted that linking the poor to banks could boost economic growth and opportunity.
"Harnessing the power of financial services can really help people to pay for schooling, save for a home, or start a small business that can provide jobs for others," Zoellick said in a statement.
"This new report on the world's 'unbanked' makes the case: the more poor people are banking today, the more they are banking on their future."
The findings were based on a survey of 150,000 people in 148 countries conducted by the US pollster Gallup.
The information is being gathered for a financial inclusion database being built by the World Bank with a 10-year grant from the Bill & Melinda Gates Foundation.
The survey found that in developing countries, polling adults at all income levels, only 37 percent of women had bank accounts, compared with 46 percent for men.
More than 80 percent said they used informal sources of credit, such as an account with a business or a loan from a friend.
"Even among those who do have a formal bank account, only 43 percent of adults use their account to save. Yet 61 percent of account holders worldwide use their account to receive payments from an employer, the government or family members living elsewhere," the World Bank said.
The research confirmed the rising popularity of using mobile phones to transfer money, banking that often does not require setting up an account at a brick-and-mortar bank.
"Mobile banking, which allows account holders to pay bills, make deposits or conduct other transactions via text messaging, has expanded to 16 percent of the market in Sub-Saharan Africa, where traditional banking has been hampered by transportation and other infrastructure problems," the Washington-based development lender said.
Kenya in particular has seen significant growth in mobile-phone banking, the report said, with 68 percent of the adults surveyed using a mobile phone for money transactions.
The World Bank has a financial inclusion portfolio of more than $3 billion, currently involved in projects in over 60 countries.
The lender supports country action plans to boost access to financial products and services through low-cost delivery mechanisms, such as mobile phones and ATM kiosks.