Why are bonds far simpler to price than stocks, and how did Treasuries overtake mortgage debt at the heart of the bond market?
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The definition of a fixed-income security
Write the definition — promised cashflows of known fixed amount at fixed dates — set it against a stock's unknown cashflows, and record that, with default set aside, present value prices nearly all of them.
The families of fixed-income securities
List Treasuries, federal agency, corporate, municipal, mortgage-backed and derivative securities with one named instrument or issuer each, and distinguish asset-backed from mortgage-related securities, with credit-card receivables, auto loans and student loans as the examples.
Amount outstanding, from mortgage-led to Treasury-led
Record mortgage-related debt's 24% lead in 2006, the 2025 U.S. total of $61.2 trillion (38.1% of $160.7 trillion worldwide) beside $68.9 trillion of U.S. equity market capitalization, and today's $31.8 trillion of Treasuries.
Stock versus flow: outstanding debt against new issuance
Define amount outstanding as a stock and issuance as a flow, then set mortgage-related debt's 34% of 2006 issuance against Treasuries' $4.8 trillion of the $11.5 trillion issued in 2025.