Major Sources of Income in Banking

1. Core Revenue Streams
   Banks generate income through several primary channels:
   Net Interest Income (NII) — the backbone of traditional banking. Banks borrow money cheaply (through deposits, paying 1–3%) and lend it at higher rates (mortgages at 6–7%, personal loans at 10–20%), pocketing the spread.
   Fee-Based Income — account maintenance fees, ATM charges, wire transfer fees, late payment penalties, and advisory fees. Large banks like JPMorgan earn tens of billions annually from fees alone.
   Trading & Investment Income — proprietary trading desks, market-making, and investment portfolios generate significant returns.
   Mortgage Origination Fees — banks charge processing, origination, and closing fees when issuing mortgages, separate from interest earned.
   Wealth Management & Brokerage — asset management fees, mutual fund sales, and insurance commissions.
2. Mortgage vs. Market Investments — The Real Comparison
   Your observation is fundamentally correct, and here is the evidence:

Factor Mortgage Lending Market Investments Average Return 3–6% net 8–15%+ potential Risk Level Low–Medium Medium–Very High Liquidity Very Low High Regulatory Capital Required High Varies Predictability High Low

Why mortgages still matter despite lower returns:
Mortgages offer predictable, long-duration cash flows that banks use to match against their long-term liabilities. They are also collateralized — if a borrower defaults, the bank seizes the property. This is why mortgage-backed securities (MBS) remain foundational to bank balance sheets.

3. Do Banks Invest in Penny Stocks?
   This is where it gets nuanced. Retail/commercial banks generally do NOT invest in penny stocks — and here is why:
   ∙ Penny stocks are unregulated, illiquid, and highly manipulable
   ∙ Banking regulators explicitly restrict speculative equity holdings
   ∙ The Basel III framework assigns extremely high risk weights to speculative equity positions, meaning banks must hold more capital against them — making such investments capital-inefficient
   Investment banks (Goldman Sachs, Morgan Stanley) do have equity trading desks, but these operate within strict Value at Risk (VaR) limits, not penny stock speculation.
4. Regulatory Restrictions — The Hard Limits
   You are absolutely right that restrictions exist. Several major frameworks govern this:
   The Volcker Rule (USA, 2015) — Part of the Dodd-Frank Act, it prohibits commercial banks from engaging in proprietary trading (trading for their own profit) with depositors’ money. Banks cannot use public deposits to speculate in markets.
   Basel III Capital Requirements — Banks must maintain:
   ∙ Common Equity Tier 1 (CET1): minimum 4.5% of risk-weighted assets
   ∙ Capital Conservation Buffer: additional 2.5%
   ∙ High-risk investments carry higher risk weights, automatically limiting how much banks can hold
   Concentration Limits — In most jurisdictions, banks cannot invest more than 10–15% of their capital in a single equity or high-risk asset class.
   Liquidity Coverage Ratio (LCR) — Banks must hold sufficient high-quality liquid assets (government bonds, cash) to survive a 30-day stress scenario, which naturally limits illiquid or risky market exposure.
5. The 2008 Crisis — Evidence of What Happens Without Restrictions
   The 2008 Global Financial Crisis is the most powerful evidence for your concern. Banks had:
   ∙ Invested heavily in mortgage-backed securities (MBS) disguised as safe instruments
   ∙ Used leverage ratios of 30:1 — borrowing $30 for every $1 of capital
   ∙ Circumvented regulations through off-balance sheet vehicles (SIVs)
   The result: over $2 trillion in losses globally, government bailouts across the US and Europe, and the collapse of Lehman Brothers. This directly led to the Basel III and Volcker Rule reforms.

Summary
Banks do invest in markets, but within a tightly regulated framework. Mortgages remain attractive not because of high returns, but because of stability, collateral security, and regulatory efficiency. The trade-off between return and risk is ultimately governed by regulators who ensure that public deposits are never fully exposed to high-risk market speculation — though history shows these guardrails are only as strong as their enforcement.