The banking system works by moving money from people who have it to people who need it: your deposits become the raw material for loans, the bank earns the spread between what it pays you and what it charges borrowers, and a layered set of federal and state rules keeps the whole arrangement from breaking when conditions turn bad. Along the way, the act of lending itself creates most of the money circulating in the economy. The mechanics are more straightforward than they look, and the details are worth knowing because they determine how safe your money is and how quickly it can move.
What Happens to Your Deposit
When you put money into a checking or savings account, the bank owes it back to you on demand or at a set date. That deposit sits on the bank’s books as a liability. The bank pools your deposit with thousands of others to build a reservoir of lendable capital far larger than any single depositor could supply, and it lends the bulk of that pool out.
The trick is maturity transformation. You can withdraw tomorrow. A homebuyer borrowing against the same pool may not finish repaying for 30 years. The bank bridges the gap by keeping enough liquid assets to cover normal withdrawals while deploying the rest into longer-term loans. When it works, it funds home purchases, business growth, and consumer spending. When confidence breaks and depositors all show up at once, you get a bank run, which is why deposit insurance and central bank backstops exist.
Before a loan gets approved, the bank evaluates the borrower’s ability to repay. Debt-to-income ratio, which compares monthly debt payments to gross income, is one of the primary metrics lenders use.1Consumer Financial Protection Bureau. What Is a Debt-to-Income Ratio? The Truth in Lending Act requires clear written disclosures of loan terms, including the annual percentage rate and finance charges, so you can compare offers.2Federal Trade Commission. Truth in Lending Act The Equal Credit Opportunity Act separately bars lenders from denying credit based on race, color, religion, national origin, sex, marital status, age, or receipt of public assistance.3Federal Trade Commission. Equal Credit Opportunity Act
Once the loan is finalized it becomes an asset on the bank’s balance sheet, and the interest the borrower pays over the life of the loan generates the revenue that keeps the bank running.
How Lending Creates Money
Banks do not hand borrowers physical dollar bills from a vault. When a bank approves a mortgage, it credits the borrower’s account with new funds. The home seller deposits that money at their own bank, which can then lend a portion of it to someone else. Each round of lending and redepositing adds to the total money in the economy.
The old textbook version of this cycle relied on reserve requirements setting a hard ceiling. That is no longer how things work. The Federal Reserve reduced reserve requirement ratios to zero percent in March 2020, eliminating mandatory reserves for all depository institutions.4Federal Reserve Board. Reserve Requirements The Fed keeps the legal authority to reimpose them, but as of 2026 the ratio remains at zero.5Federal Register. Reserve Requirements of Depository Institutions
What stops a bank from lending infinitely, then, is capital requirements and liquidity. Banks also hold high-quality government bonds and other liquid instruments they can sell quickly if withdrawal demand spikes. No bank holds enough to pay every depositor at once. That built-in vulnerability is exactly why the safety net around banking exists.
How Banks Earn Money
The main revenue engine is the net interest margin: the gap between what the bank pays you on savings and what it charges borrowers on mortgages, auto loans, credit cards, and business loans. If it pays depositors 2 percent and lends at 6 percent, that 4 percent spread covers operating costs, absorbs loan losses, and produces profit. Federal Open Market Committee decisions on the federal funds rate ripple through both sides. When the Fed raises its target, banks tend to raise lending rates faster than deposit rates, which can widen the margin for a while.
Interest is not the whole picture. Banks also earn fee income from account maintenance, overdrafts, wire transfers, wealth management, and credit card interchange. At the largest institutions, trading and investment banking advisory fees add another layer. These non-interest streams have grown significantly, and at some large banks they rival lending as a source of revenue.
Overdraft fees have drawn recent regulatory attention. The Consumer Financial Protection Bureau finalized a rule that, effective October 1, 2025, treats overdraft charges above $5 at institutions with more than $10 billion in assets as credit subject to full lending disclosure requirements.6Consumer Financial Protection Bureau. Overdraft Lending: Very Large Financial Institutions – Final Rule Smaller banks and credit unions are outside that rule, and their overdraft fees still commonly land between $25 and $35 per occurrence.
How Your Money Is Protected If the Bank Fails
If your bank fails, the Federal Deposit Insurance Corporation covers your deposits up to $250,000 per depositor, per insured bank, for each ownership category.7FDIC.gov. Deposit Insurance At A Glance The limit has held since 2008, and it applies whether you keep a checking account, savings account, money market deposit account, or certificate of deposit.8FDIC.gov. Understanding Deposit Insurance
Ownership category matters more than most people realize. A joint account is insured up to $250,000 per co-owner, so a married couple sharing one joint account has $500,000 in coverage at a single bank. Certain retirement accounts like IRAs get a separate $250,000 per owner. Trust accounts with named beneficiaries are covered at $250,000 per owner per beneficiary, capped at $1,250,000 per owner across all trust accounts at the same bank.7FDIC.gov. Deposit Insurance At A Glance
FDIC insurance does not cover investments like stocks, bonds, mutual funds, annuities, life insurance policies, or cryptocurrency.8FDIC.gov. Understanding Deposit Insurance If your bank sells you a mutual fund at a branch, that fund is not insured.
Credit unions carry equivalent protection through the National Credit Union Share Insurance Fund, administered by the NCUA. The coverage limit matches the FDIC’s at $250,000 per member per ownership category.9MyCreditUnion.gov. Share Insurance
How Banks Themselves Are Kept Safe
The United States runs a dual banking system, meaning a bank can be chartered either by the federal government or by a state. A nationally chartered bank is licensed by the Office of the Comptroller of the Currency and supervised under federal law. A state-chartered bank is licensed by its state banking regulator and is still subject to federal rules if it carries FDIC insurance or belongs to the Federal Reserve System.10OCC.gov. National Banks and the Dual Banking System Regardless of who issues the charter, banks face the same core safety and soundness constraints.
Capital Requirements
With reserve requirements at zero, capital requirements have become the main constraint on how aggressively banks can lend. Every bank must hold a minimum amount of high-quality capital against its risk-weighted assets. The baseline minimum for Common Equity Tier 1 capital is 4.5 percent, plus a stress capital buffer of at least 2.5 percent. The largest globally significant banks carry an additional surcharge of at least 1 percent on top of that.11Federal Reserve Board. Annual Large Bank Capital Requirements To be considered “well capitalized” under the prompt corrective action framework, a bank must maintain a leverage ratio of at least 5 percent.12Federal Register. Regulatory Capital Rule: Modifications to the Enhanced Supplementary Leverage Ratio Standards
Capital is the bank’s own money at risk. When a loan goes bad, the loss comes out of capital, not out of depositors’ funds. Higher capital requirements mean a bigger cushion before the bank becomes insolvent.
Stress Tests
Banks with $250 billion or more in total assets must run stress tests under the Dodd-Frank Act, simulating how their balance sheet would hold up under severe scenarios such as a deep recession or a sharp jump in unemployment. The OCC issues the scenarios each year, and banks publish their results.13OCC.gov. Dodd-Frank Act Stress Test (Company Run) The stress capital buffer is derived from these results, so a bank that performs poorly faces a higher capital requirement as a direct consequence.
The Discount Window
When a bank needs short-term cash and can’t get it from other banks, it can borrow directly from the Federal Reserve through the discount window. This is the lender-of-last-resort function, and it exists so that temporary cash crunches don’t cascade into broader failures. Banks pledge collateral to borrow, and the rate they pay is typically above the market rate to discourage overreliance.14Federal Reserve Board. Discount Window
Compliance Exams
Federal regulators run regular examinations to verify compliance with laws like the Bank Secrecy Act, which requires banks to detect and report suspicious activity that could signal money laundering or terrorist financing.15OCC.gov. Bank Secrecy Act and Anti-Money Laundering Examinations Examiners review the bank’s compliance program, test its transaction monitoring, and assess whether its controls match its risk profile.16FFIEC BSA/AML Manual. Assessing Compliance with BSA Regulatory Requirements – Introduction Banks that fail can face fines in the millions or, in extreme cases, lose their operating license.
How Money Moves Between Banks
When you send money to someone at a different bank, two steps happen behind the scenes. Clearing is where the banks exchange transaction details and verify funds; a clearinghouse in the middle nets out the balances so only the difference has to change hands. Settlement is the actual transfer of value between the banks’ accounts, typically held at the Federal Reserve.
ACH
The Automated Clearing House network handles batch processing of direct deposits, recurring bill payments, and person-to-person transfers. Your employer sends payroll instructions to its bank, that bank packages them with files from other companies, and an ACH operator sorts everything and routes it to the receiving bank.17Nacha. How ACH Payments Work It’s cheap and efficient, but not instant. Payments typically settle in one to two business days on scheduled batch cycles.
Wire Transfers
For high-value or time-sensitive payments, banks use wire networks. The Federal Reserve operates Fedwire, which provides real-time gross settlement for large-dollar transfers between institutions. Unlike ACH, each Fedwire transaction settles individually and irrevocably as it is processed. Domestic outgoing wires typically cost $25 to $30 at major banks, and international wires often run $45 or more.
For international transfers, the remittance transfer rule under Regulation E requires banks to disclose all fees, applicable taxes, the exchange rate, and the exact amount the recipient will receive, before you authorize the transfer.18Consumer Financial Protection Bureau. Regulation E – Section 1005.31 Disclosures A bank cannot list the exchange rate as “unknown” or “to be determined.”
FedNow
The Federal Reserve launched the FedNow Service in July 2023 to enable instant payments that settle within seconds at any time of day, any day of the year.19Federal Reserve Board. FedNow Service – Frequently Asked Questions Unlike ACH, FedNow settles each payment individually and immediately. The service is still in its adoption phase, with roughly 9,000 banks and credit unions in the country gradually joining.
Your Rights When Something Goes Wrong
If someone drains your checking account with an unauthorized debit card transaction, your liability depends almost entirely on how fast you report it. Under the Electronic Fund Transfer Act, you are liable for no more than $50 if you notify the bank within two business days of learning about the unauthorized transfer. Report after two days but within 60 days of receiving your statement, and your exposure jumps to $500. After 60 days you could be on the hook for the full amount.
For any error on your account, including unauthorized charges, incorrect amounts, or missing deposits, Regulation E gives you 60 days from when the bank sends your statement to report it. The bank then has 10 business days to investigate and resolve the problem. It can take up to 45 days if it needs more time, but only if it provisionally credits your account within those first 10 business days so you are not left without the money while the investigation runs.20Consumer Financial Protection Bureau. Regulation E – Section 1005.11 Procedures for Resolving Errors
Check deposits have their own timing rules under Regulation CC. Cash and electronic payments must generally be available the next business day. Government checks, cashier’s checks, and similar official instruments deposited in person are also available the next business day. Personal and business checks may be held for two to five business days depending on the type of check and how it was deposited.21eCFR. Part 229 Availability of Funds and Collection of Checks (Regulation CC) Deposits at ATMs that don’t belong to your bank can be held up to five business days. Banks can extend holds further in specific circumstances, such as when they have reason to doubt the check will clear or when the deposit is unusually large.
The Different Kinds of Institutions Holding Your Money
Not every place that looks like a bank actually is one. Commercial banks are the for-profit institutions most people picture. They are chartered at the federal or state level, insured by the FDIC, and regulated by some combination of the OCC, the Federal Reserve, and state banking departments. Their profits flow to shareholders.
Credit unions are nonprofit cooperatives owned by their members. Because they are not chasing shareholder returns, they often offer lower loan rates, higher savings rates, and fewer fees. They are chartered and regulated by the NCUA at the federal level or by state regulators, and their deposits are insured through the NCUA’s share insurance fund rather than the FDIC.22MyCreditUnion.gov. How Is a Credit Union Different Than a Bank Coverage is the same $250,000 per member per ownership category.9MyCreditUnion.gov. Share Insurance
Neobanks and fintech companies are the newest entrants. Names like Chime, Current, and SoFi deliver bank-like services through smartphone apps, but many of them are not actually banks. They partner with FDIC-insured banks that hold the deposits behind the scenes. Your money may be protected through pass-through FDIC insurance, but the details depend on how the neobank structures its accounts. If you use one, verify which FDIC-insured institution actually holds your funds and confirm your coverage before keeping large balances there.