How Banks Operate

A bank looks simple from the customer side. Money comes into an account, payments go out, savings may earn interest, and loans provide funds that can be repaid over time. Behind those familiar services is a balance-sheet business that has to fund assets, process payments, manage liquidity, absorb credit losses and maintain enough capital to keep operating through periods of stress.

The most useful way to understand how banks operate is therefore not to picture a vault that receives deposits and hands the same cash to borrowers. Commercial banks connect savers, borrowers and payment systems, but the connection is managed through accounting entries, funding markets and risk controls. Banking itself is essentially the management of financial resources, and for a commercial bank those resources appear on both sides of its balance sheet.

Different banks perform different jobs

The word bank covers institutions with very different purposes. central banks such as the Federal Reserve sit at the center of monetary and payment systems, while retail or commercial banks take deposits, extend credit and provide payment services to households and businesses. investment banks focus more heavily on securities issuance, capital raising, advisory work, trading and market activity.

This article is mainly about commercial banking because that is the model most people encounter when they open a checking account, receive a salary deposit, use a debit card or apply for a loan. Large banking groups can combine commercial banking with wealth management, securities businesses and other financial activities, so the legal entity that holds a customer’s deposits is not necessarily doing everything associated with the wider banking group.

A bank is a balance-sheet business

A commercial bank’s balance sheet explains most of its economics. Loans, securities, cash and balances held with other institutions are assets because they represent value the bank owns or amounts others owe it. Deposits and other borrowings are liabilities because they represent amounts the bank owes to customers or other funding providers, while shareholders’ equity is the residual interest that remains after liabilities are deducted from assets.

The scale of those categories is visible in the Federal Reserve’s H.8 data. For the week ending July 29, 2026, U.S. commercial banks held about $25.6 trillion of assets, including roughly $13.9 trillion of loans and leases and $5.8 trillion of securities, while deposits were about $19.4 trillion.^[1] Those figures make two points that the simple deposit-and-loan story misses: banks own large securities portfolios as well as loans, and deposits are a major funding source without being the bank’s only liability.

Balance sheets also show why a bank cannot judge itself by whether an individual loan is profitable. A bank may hold mortgages that run for decades, business loans with different repayment schedules, securities that change in market value, cash needed for daily payments and a large volume of deposits that customers can move with little notice. Management has to make all of those positions work together rather than treating each product as a self-contained transaction.

What happens when you deposit money

When a customer deposits money, the money on deposit becomes a liability of the bank to that customer. The customer has an account balance and a contractual claim on the bank, while the bank receives an asset such as cash or a reserve balance depending on how the deposit arrived. The bank does not normally set aside each customer’s money in a separate pile and wait for the same customer to withdraw it later.

Deposits are valuable to banks because they provide funding and because transaction accounts create long-term customer relationships. A bank can use its overall pool of funding to support loans, securities holdings, payment obligations and other assets, while keeping enough liquid resources to meet expected withdrawals and transfers. The maturity mismatch between relatively withdrawable deposits and longer-term assets is one of the defining features of commercial banking and one reason liquidity management matters so much.

Interest paid on deposits is part of the bank’s funding cost. A bank deciding what rate to offer on savings accounts or certificates of deposit has to consider competition for deposits, market interest rates, how much funding it needs and what alternative sources of funding would cost. A checking account that pays little or no interest may still be costly to service because the bank provides payments, fraud controls, statements, customer support and access through branches, ATMs or digital channels.

Banks do not simply lend out a fixed share of deposits

The traditional explanation of fractional-reserve banking often says that a bank keeps a fixed fraction of deposits in reserve and lends the rest. That can be a useful historical teaching device, but it is not an accurate description of current U.S. reserve requirements. The Federal Reserve reduced reserve requirement ratios on transaction accounts to zero percent in March 2020, and the requirement has remained at zero.^[2]

Zero reserve requirements do not mean a bank can lend without limits or operate without liquid assets. A bank still needs funding, payment capacity and access to liquidity, and it remains constrained by capital requirements, risk limits, credit quality, market conditions, customer withdrawals and supervisory expectations. A bank that expands assets aggressively without a stable way to fund them can create serious problems even if no mechanical reserve ratio prevents the expansion.

The distinction matters because bank lending is not a process in which officers first find a particular depositor’s dollars and then pass those dollars to a borrower. When a bank approves a loan and credits the borrower’s deposit account, it records a loan asset and a corresponding deposit liability. If the borrower later sends those funds to someone at another bank, the originating bank then has to settle the payment and manage the resulting funding and liquidity effects.

Deposits still matter enormously. They are usually a relatively stable and often comparatively low-cost form of funding, which can make a bank more competitive in lending money at interest. The important correction is that deposits, lending and settlement are linked through the bank’s whole balance sheet rather than through a one-for-one recycling of particular customer deposits.

How bank lending works

Banks extend many different types of loans, including mortgages, business credit, auto loans, personal loans and revolving credit. Before extending credit, the bank assesses the borrower’s ability and willingness to repay, the value of any collateral, the purpose and structure of the loan and how the exposure fits within the bank’s broader portfolio. The underwriting standard is not identical across products because the risks of a secured mortgage, an unsecured consumer loan and a commercial credit line are not identical.

A credit card is a clear example of bank credit because the issuer allows the cardholder to borrow up to an approved limit and repay according to the account terms. A debit-card purchase is different: it normally draws on money in a deposit account rather than creating a loan to the cardholder, even though the payment itself may involve authorization, clearing and settlement between financial institutions.

Mortgages are important to bank lending, but it is inaccurate to assume that every mortgage stays on the originating bank’s balance sheet for its entire life. Banks can retain loans, sell them, securitize eligible loans or service loans for other investors. The choice affects interest-rate exposure, credit risk, liquidity and how much balance-sheet capacity remains available for new lending.

Loan pricing is not simply the deposit rate plus a fixed profit margin. Banks have to consider their funding cost, expected credit losses, operating expenses, required capital, the term and structure of the loan, competitive conditions and the return they need for taking the risk. Two borrowers seeking the same dollar amount can therefore receive different terms because the economic risk of the two loans is not the same.

Payments connect one bank to the rest of the system

Another central function of a bank is to facilitate financial transactions. A customer may see only an account balance changing, but the bank has to receive and send payment instructions through card networks, ACH, wire systems, checks or instant-payment rails. Payments between customers of the same bank can often be handled through internal bookkeeping, while payments to another bank require an interbank settlement process.

Authorization, clearing and settlement do not always happen at the same time. A card purchase can be authorized in seconds and settle later, an ACH entry may settle in a batch, a wire can settle individually in real time, and an instant payment can combine messaging and final settlement within seconds. The idea that every electronic payment waits a day or two is therefore too broad, just as the idea that every payment is instantly final is too broad.

Payment activity also affects liquidity. If many customers send funds to accounts at other banks, the bank must be able to meet the outgoing settlement obligation even though its longer-term assets, such as mortgages and business loans, cannot be turned into cash immediately without cost. This is why a bank holds liquid assets, forecasts payment flows and maintains access to additional funding rather than trying to maximize the share of its balance sheet invested in the highest-yielding assets.

How banks make money

Net interest income is one of the main sources of earnings for a traditional commercial bank. The bank earns interest on loans and securities and pays interest on deposits and other borrowings, with the difference contributing to net interest income. The relationship is affected by both the level of interest rates and the timing with which asset yields and funding costs adjust, so rising market rates do not automatically increase a bank’s profit.

Noninterest income is another important part of the model. Banks can earn fees from payments, cards, account services, wealth management, loan servicing, treasury services, advisory work and other activities, although the mix varies widely by institution. Larger and more diversified banks may rely less on traditional interest spreads than a community bank whose business centers on deposits and local lending.

Revenue is only the beginning of the profit calculation. A bank has payroll, technology, branches, compliance costs, fraud losses and other operating expenses, and it must recognize expected or realized losses when borrowers do not repay. Strong revenue growth can therefore coexist with weak earnings if credit losses or funding costs rise enough, while a conservative bank with slower asset growth can remain highly profitable if its funding and credit performance are favorable.

Capital and liquidity protect against different problems

Capital and liquidity are sometimes discussed as though they were interchangeable cushions, but they protect against different problems. Capital absorbs losses and represents the owners’ stake in the bank, so loan losses or declines in asset values reduce equity before they threaten creditors. Liquidity concerns the bank’s ability to meet cash and payment obligations when they come due without having to sell assets at unacceptable losses or lose access to funding.

A bank can be solvent in the sense that the value of its assets exceeds its liabilities and still experience a liquidity crisis if too many funding providers demand cash at once. The reverse problem is also possible: a bank can have plenty of cash today but still be economically weak if losses have eroded the value of its assets and capital. Bank management and regulators therefore watch both the amount and quality of capital and the stability and availability of funding.

Deposit insurance reduces the incentive for insured depositors to run at the first sign of trouble. At an FDIC-insured U.S. bank, the standard insurance amount is $250,000 per depositor, per insured bank, for each account ownership category.^[3] Coverage rules matter because multiple accounts at the same bank are not automatically separate for insurance purposes, while different ownership categories can receive separate coverage when the requirements are met.

The risks banks have to manage

Credit risk is the most obvious banking risk because borrowers can fail to repay, but it is not the only one. Banks also face interest-rate risk when the rates or maturities on assets and liabilities respond differently to market changes, liquidity risk when funding becomes harder to obtain, operational risk from systems and processes, and compliance risk when products or conduct violate applicable rules. These risks interact rather than appearing in isolation.

Interest-rate risk provides a useful example. A bank may fund itself with deposits whose rates can rise quickly while holding long-term fixed-rate loans and securities whose income changes little. If funding costs rise faster than asset yields, the interest margin can narrow, and higher market yields can also reduce the market value of existing fixed-rate securities. The bank therefore has to manage both earnings sensitivity and the economic value of its balance sheet.

Credit risk also has a portfolio dimension. A collection of individually reasonable loans can still be dangerous if too many depend on the same industry, geographic area, property type or economic assumption. Diversification, lending limits, collateral standards and ongoing monitoring are intended to prevent one adverse development from damaging too much of the balance sheet at once.

Banks also invest and provide market services

Commercial banks do not hold only loans and cash. Securities are a significant part of banking assets and can serve several purposes, including liquidity management, income generation and balance-sheet positioning. The mix depends on the institution, and securities that appear safe from a credit perspective can still expose the bank to interest-rate and market-value risk.

Banking groups can also provide brokerage, custody, wealth management and capital-markets services. Investment-banking affiliates may help companies raise capital by underwriting securities, while broker-dealer businesses can execute client transactions and make markets. Banks involved in trading in securities operate under rules and risk controls that differ from ordinary deposit taking and consumer lending, even when the businesses sit under the same corporate umbrella.

That distinction is important because a deposit customer, a borrower and an institutional markets client can all be dealing with the same banking group for very different reasons. Commercial banking is built around deposits, credit and payments, while securities businesses are more directly tied to capital markets. Treating every activity of a diversified financial group as if it were simply an extension of the checking-account business makes the institution harder rather than easier to understand.

What the customer sees is only the front end

For a customer, a bank is an account, an app, a card, a branch and perhaps a lender. For the institution, each of those services creates balance-sheet entries, payment obligations, funding needs, operational costs and risks that have to fit together. A checking account is both a service to the customer and a liability that funds the bank, while a loan is both useful credit to the borrower and an asset whose return has to compensate the bank for funding, expenses and risk.

The clearest mental model is therefore a managed balance sheet rather than a warehouse for money. Deposits are central to bank funding, but banks also borrow elsewhere; loans are major assets, but banks also hold securities and cash; payments move customer money, but they also create settlement and liquidity demands. Capital provides loss-absorbing capacity, liquidity keeps obligations payable, and risk management determines how aggressively the institution can use its balance sheet.

That framework also explains why banks can look stable for long periods and then come under pressure quickly when funding costs, credit conditions, market values or depositor behavior change. Banking works because short-term, money-like liabilities can support longer-term financial assets, but that transformation has to be managed carefully. The everyday convenience of deposits, lending and electronic payments rests on a business that is continuously balancing profitability against the need to remain liquid, solvent and trusted.