You deposit £1,000 in your bank account.
The bank pays you 2% interest. £20 per year.
Then the bank lends your £1,000 to someone else at 6% interest. £60 per year.
The bank pockets the £40 difference — doing nothing except sitting between you and the borrower.
Now multiply that by trillions of dollars across hundreds of millions of accounts globally. You begin to understand why banking is one of the most consistently profitable industries in human history — and why the largest banks in the world generate tens of billions in profit annually despite appearing, on the surface, to simply look after other people’s money.
But the interest rate spread is only the beginning. Modern banks make money in ways that most of their customers never think about — some straightforward, some extraordinarily complex, some that played a direct role in triggering the worst financial crisis since the Great Depression.
This is the plain-English guide to how banks actually make money.
The Foundation: Net Interest Income
The core business of a bank has not changed significantly since the Medici family ran the most powerful banking network in 15th-century Florence: borrow money cheaply, lend it out expensively, keep the difference.
This difference — the spread between what a bank pays depositors and what it charges borrowers — is called net interest income (NII). It is the foundation upon which everything else is built.
The mechanics are simple. A bank receives deposits from customers — savings accounts, current accounts, certificates of deposit. It pays these depositors interest. It then lends that money out as mortgages, personal loans, car loans, business loans, and credit card balances, charging higher interest rates to borrowers than it pays to depositors.
The spread between these two rates is the bank’s raw material for profit.
In practice, this spread varies significantly based on:
The interest rate environment. When central banks set rates high, lending rates rise faster than deposit rates — widening the spread and boosting bank profitability. This is why bank stocks typically perform well in rising interest rate environments. Conversely, near-zero interest rates (as in 2009-2021) compressed spreads and squeezed net interest income significantly.
Credit quality. Banks charge higher interest rates to riskier borrowers — those with lower credit scores, less collateral, or less stable income. A secured mortgage to a high-income borrower might be priced at 4-5%. An unsecured personal loan to a borrower with poor credit might be priced at 15-25%. The higher rate compensates for the higher probability of default.
Loan type. Mortgages typically carry lower rates (secured against property, low default risk). Credit cards carry dramatically higher rates (unsecured, high default risk). Business loans fall somewhere in between, varying by the creditworthiness of the business.
For the largest global banks — JPMorgan Chase, Bank of America, HSBC, BNP Paribas — net interest income accounts for roughly 50-60% of total revenue. It is the bedrock.
Fractional Reserve Banking: The Multiplier That Makes It All Work
Here is the part of banking that most people find either ingenious or alarming, depending on their perspective.
When you deposit £1,000 in a bank, the bank does not keep your £1,000 sitting in a vault. It lends most of it out.
In a fractional reserve banking system, banks are required to keep only a fraction of their deposits as reserves — held either in their own vaults or at the central bank. The rest can be lent out.
If the reserve requirement is 10%, a bank receiving £1,000 in deposits must keep £100 in reserve but can lend out £900. That £900, when deposited in another bank, can be lent out again (minus 10% reserve) — creating another £810 in loans. Which creates another £729 in loans. And so on.
This process — called the money multiplier — means that a banking system with a 10% reserve requirement can, in theory, create up to £10,000 in loans from an initial £1,000 deposit. The bank creates money through the act of lending.
This is not a conspiracy theory or a secret. It is the documented, publicly stated mechanism by which modern banking systems operate. The Bank of England published a paper in 2014 explicitly explaining that “banks create money in the form of bank deposits by making new loans.”
The implications are profound:
- Banks profit not just from existing money but from money they effectively create
- The system depends entirely on depositors not all demanding their money back simultaneously
- When confidence breaks down — as in the 2008 financial crisis — the entire mechanism can seize
This last point is why central banks exist as “lenders of last resort” — to provide emergency liquidity when the system’s inherent fragility becomes exposed.
Fee Income: The Second Revenue Stream
Beyond interest, modern banks generate substantial revenue from fees. This category has grown dramatically over recent decades as regulatory pressure and competition compressed interest margins.
Account fees. Monthly maintenance fees, overdraft fees, wire transfer fees, foreign transaction fees. Small per-transaction amounts that aggregate to significant revenue across millions of accounts. Overdraft fees alone generate billions of dollars annually for US banks.
Credit card fees. Banks that issue credit cards earn revenue from multiple sources simultaneously: the interest charged to cardholders who carry balances, the annual fees charged to cardholders, and — perhaps most significantly — the interchange fees charged to merchants every time a card is used. When you pay for a £50 dinner with a Visa credit card, the restaurant’s bank pays your bank a fee of roughly 1.5-2%. Your bank collects this whether you pay your balance in full or not.
Loan origination fees. When a bank originates a mortgage or business loan, it typically charges fees at closing — a percentage of the loan value paid upfront by the borrower. On a £200,000 mortgage, a 1% origination fee generates £2,000 in immediate income before a single interest payment is made.
Wealth management and advisory fees. Banks with private banking and wealth management arms charge fees for investment advice, portfolio management, and financial planning. These are typically a percentage of assets under management — 0.5% to 1.5% annually — and generate highly recurring, predictable revenue.
Safety deposit boxes, wire transfers, currency exchange. Individually minor but collectively meaningful revenue streams from everyday banking services.
For large universal banks, fee income typically represents 30-40% of total revenue — making it a critical complement to interest income and a buffer when rate environments compress NII.
Investment Banking: The High-Stakes Third Stream
The largest global banks — Goldman Sachs, Morgan Stanley, JPMorgan, Deutsche Bank, Barclays — operate significant investment banking divisions alongside their retail banking operations. This is where the numbers get very large and the complexity increases dramatically.
Underwriting. When a company wants to issue new shares (an IPO or secondary offering) or issue bonds, it typically hires an investment bank to manage the process. The bank buys the securities from the company and sells them to investors, earning an underwriting fee — typically 3-7% of the total value of the deal. A $1 billion IPO at 5% underwriting generates $50 million in fees from a single transaction.
Mergers and acquisitions (M&A) advisory. When companies merge, acquire other companies, or are sold, they hire investment banks to advise on valuation, deal structure, negotiation, and execution. Advisory fees on major deals typically range from 0.5% to 2% of transaction value. A $10 billion merger generates $50-200 million in advisory fees.
Trading. Investment banks operate trading desks that buy and sell securities — stocks, bonds, currencies, commodities, derivatives — on behalf of clients (earning bid-ask spreads and commissions) and sometimes on their own account (proprietary trading). Trading revenue is volatile — it can be extremely high in active markets and sharply negative in dislocated ones.
Structured products. Investment banks create and sell complex financial instruments — collateralised debt obligations (CDOs), credit default swaps, interest rate derivatives, structured notes. These products generate significant fees and can be highly profitable. They also, as demonstrated in 2008, can concentrate catastrophic risk in ways that are not apparent until the moment of crisis.
The 2008 Crisis: How the Model Broke
The 2008 financial crisis was, at its core, a story of the banking business model being pushed to its logical extreme — and then past it.
The sequence of events:
US banks, flush with liquidity from low interest rates and growing demand from global investors for yield, dramatically expanded their mortgage lending — including to borrowers who had little ability to repay. These “subprime” mortgages were then packaged into securities (mortgage-backed securities and CDOs) and sold to investors globally. This process — securitisation — allowed banks to generate origination fees, sell the risk off their balance sheets, and lend again. The model incentivised volume over quality.
Rating agencies, paid by the banks that created the securities, rated many of these products as investment grade. Insurance companies — most notably AIG — sold credit default swaps (essentially insurance contracts) guaranteeing these securities without holding sufficient capital to pay out if they failed.
When US house prices began falling and mortgage defaults rose, the securities backed by those mortgages began losing value. Banks and investors holding these securities faced massive losses. Confidence in the value of complex financial instruments collapsed. Banks stopped trusting each other. The interbank lending market froze. Credit to the broader economy seized.
The result: a near-collapse of the global financial system, requiring unprecedented government intervention — $700 billion in the US alone — to prevent a complete breakdown.
The 2008 crisis did not reveal that banking was fraudulent. It revealed that the incentive structures of modern banking — where fees are earned upfront and risk is transferred to others — can produce catastrophic outcomes when the alignment between risk-taking and risk-bearing breaks down completely.
How Banks Are Regulated
The catastrophe of 2008 accelerated a global regulatory overhaul of banking, centred on two frameworks:
Basel III: International banking standards that require banks to hold more capital against their risky assets. The core principle: if banks must put more of their own money at risk, they will take less risk. Capital requirements increased significantly post-2008, making banks more resilient but also somewhat less profitable.
Stress testing: Major banks are now required to demonstrate — through regular stress tests conducted by regulators — that they could survive severe economic scenarios without failing. Banks that fail stress tests face restrictions on dividends and buybacks until they improve their capital positions.
Deposit insurance: In most developed countries, deposits are insured up to a limit (£85,000 in the UK, $250,000 in the US) by government-backed schemes. This eliminates the incentive for depositors to run at the first sign of trouble — which was a primary mechanism of bank failures in the Great Depression.
Separation of retail and investment banking: Following 2008, several countries introduced rules limiting the ability of retail banks to engage in proprietary trading and speculative activities that could put depositor funds at risk. In the UK, the ring-fencing rules require large banks to separate their retail banking from their investment banking operations.
These regulations have made the banking system meaningfully safer than it was in 2008 — though not immune to crisis, as the 2023 failures of Silicon Valley Bank and Credit Suisse demonstrated.
The Fintech Challenge
The traditional banking model faces its most significant structural challenge in decades from financial technology companies — fintechs — that are unbundling banking’s revenue streams.
Where a traditional bank earns fees across dozens of product categories — current accounts, mortgages, credit cards, investments, foreign exchange — fintechs attack one or two categories with a better product at lower cost.
Revolut and Wise have taken significant share of international money transfer revenue by offering near-interbank exchange rates. Monzo and Starling offer current accounts with superior user experiences and lower fees. PayPal and Stripe have taken significant merchant payment processing. Robinhood and eToro have compressed brokerage commissions toward zero.
Traditional banks are responding — primarily through their own digital offerings, acquisitions of fintech companies, and the advantages of scale, trust, and regulation that fintechs cannot easily replicate. The outcome of this competition will shape the financial services industry for the next decade.
What is clear: the fat, unchallenged fees that characterised banking for decades are being compressed by competition. The banks that survive and thrive will be those that can combine the trust and regulatory stability of traditional banking with the user experience and efficiency of digital-native competitors.
What This Means for You as a Bank Customer
Understanding how banks make money changes how you should interact with them.
Your deposit is a resource they use. Every pound in a savings account earning 0.5% while the bank lends at 5% is a transfer of wealth from you to the bank. Move idle savings to higher-yield accounts, money market funds, or short-term government bonds wherever possible.
Overdraft fees are extraordinarily expensive. A £35 overdraft fee on a £100 overdraft for a week is an annualised interest rate of over 1,800%. Banks earn disproportionately from customers who manage their accounts poorly. Avoid overdrafts.
Credit card rewards are funded by merchant fees and by revolvers. The points and cashback on premium credit cards are funded by the interchange fees merchants pay and by the interest paid by customers who carry balances. If you pay in full every month, you are net benefiting from the system at merchants’ expense. If you carry a balance, you are subsidising other cardholders.
Your mortgage rate has significant room to negotiate. Banks price mortgages with margin above their cost of funds. Borrowers with strong credit profiles, significant deposits, and the willingness to shop across lenders or use a mortgage broker regularly secure materially better rates than those who simply accept the first offer.
Loyalty is rarely rewarded in banking. Banks offer their best rates to new customers. Long-standing customers who do not regularly review their products typically pay above-market rates on mortgages, earn below-market rates on savings, and pay unnecessary fees. Review your products annually.
The Bottom Line
Banking is a business. A highly profitable, deeply interconnected, systemically important business — but a business nonetheless.
It makes money by sitting between borrowers and savers, collecting the spread. It makes money from fees on every transaction, every account, every piece of advice. It makes money from the complex machinery of capital markets. And it does all of this using money that is, in a meaningful sense, created through the act of lending.
Understanding this does not require you to be suspicious of banks. It requires you to engage with them as an informed participant rather than a passive one.
The bank is optimising for its own returns. You should be optimising for yours.
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