What's the difference between an investment bank and a commercial bank?
A commercial bank takes deposits and makes loans. An investment bank advises on M&A and capital raising, underwrites securities, and helps institutional clients access capital markets; universal banks do both.
Intuition
Commercial banks transform balance sheets — turning short-duration, low-cost deposits into longer-duration credit exposure, so their economics are spread-and-risk driven. Investment banks transform information and access, reducing frictions between capital seekers and providers, so their economics are fee-and-flow driven. That is why one carries assets and manages default risk while the other earns at the point of transaction.
Watch
Expect a follow-up on how Glass-Steagall's repeal (1999 Gramm-Leach-Bliley) and post-2008 rules changed this — universal banks combine both, but the divisions still differ: commercial is capital-intensive and NII-driven, IB is capital-light and fee-driven.
Deep Dive
Distinguish how investment banks and commercial banks make money, what they do, and how they connect to different parts of the financial system.
The core split comes down to which side of the capital markets each bank sits on and how each generates revenue.
| Dimension | Commercial Bank | Investment Bank |
|---|---|---|
| Core function | Takes deposits, makes loans | Advises on transactions, underwrites securities |
| Primary revenue | Net Interest Income: spread between lending and deposit rate, $ NII = r_{loan} - r_{deposit} $ applied to the loan book | Fee-based: advisory fees (M&A), underwriting spreads (ECM/DCM), trading commissions |
| Balance sheet role | Principal — uses own balance sheet to lend, holds credit risk | Agent/intermediary — connects issuers to investors; balance sheet used selectively (bridge loans, prop) |
| Clients | Individuals, small/mid-size businesses, corporates | Corporations, institutional investors, governments, PE/sponsors |
| Key risk | Credit risk and interest rate risk (asset-liability mismatch) | Market risk, reputation risk, deal-flow cyclicality |
| Regulatory regime | Heavy — reserve requirements, FDIC, Basel capital ratios | Historically lighter; post-2008 BHCs face similar capital rules |
| Funding source | Customer deposits (cheap, stable) | Wholesale funding, repo, equity capital |
How they connect mechanically:
- Commercial bank lends $500M via a revolver → earns $ \text{SOFR} + 200\text{bps} $ minus cost of deposit funding.
- IB advises same company on a $2B acquisition → earns 0.5%-1.0% advisory fee, then underwrites a $1B bond → earns ~1%-2% underwriting spread.
- Commercial bank bears ongoing credit risk for years; IB earns its fee at close and moves on (unless holding a bridge).
Post-Glass-Steagall reality (post-1999 GLBA / post-2008):
- Universal banks (JPM, BofA, Citi) combine both under one holding company.
- Internally: commercial division is capital-intensive and NII-driven; IB division is capital-light and fee-driven.
- Regulators still treat the activities differently for capital allocation and stress testing.
Shortcut: Commercial banks earn the spread on lending their own money; investment banks earn fees for helping others raise or deploy money.