SIE Ready💵 Debt Securities · Lesson 5 of 7 · 6 min
Ginnie, Fannie, Freddie and the Mortgage Pool
🏠 When homeowners refinance, mortgage bond investors get their money back early, right when they least want it.
💡 Key idea
Only Ginnie Mae carries the U.S. government's full faith and credit. Falling rates bring prepayment risk; rising rates bring extension risk.
🧠 Why it matters
Agency MBS are pools of home mortgages whose principal and interest pass through to investors, usually monthly. GINNIE MAE (GNMA) guarantees timely payment on MBS backed by FHA, VA and USDA loans, and that guarantee carries the FULL FAITH AND CREDIT of the U.S. government. FANNIE MAE (FNMA) and FREDDIE MAC (FHLMC) are government-sponsored enterprises: they guarantee their MBS, but not with full faith and credit. PREPAYMENT RISK: when rates fall, homeowners refinance and principal returns early, to be reinvested at lower rates. EXTENSION RISK: when rates rise, prepayments slow and the investor's money stays tied up longer. A CMO slices pool cash flows into TRANCHES with different priorities and expected maturities, so each tranche carries a different mix of these risks.
📈 In the real world
📬 Mr. Tran owns a pool of mortgage pass-throughs. Rates drop two points, his monthly checks suddenly jump as borrowers refinance, and he must reinvest that principal at lower yields. His neighbor's CMO tranche, designed to absorb prepayments last, barely changed. Same mortgages, different slice.
📌 Takeaways
- GNMA = full faith and credit; FNMA and FHLMC = GSEs, not full faith and credit
- Rates down → prepayment risk; rates up → extension risk
- CMO tranches divide cash flows and risks by priority
📖 Terms in this lesson
Ginnie Mae (GNMA): A government agency whose guaranteed mortgage-backed securities carry the full faith and credit of the US government.
Fannie Mae and Freddie Mac: Government-sponsored enterprises whose mortgage-backed securities are not backed by the full faith and credit of the US government.
Collateralized mortgage obligation (CMO): A mortgage-backed security split into tranches that receive principal in a set order and carry different prepayment risks.
Prepayment risk: The risk that homeowners repay mortgages faster when rates fall, returning principal to mortgage-backed investors early.
GINNIE IS THE GOVERNMENT'S: Of the mortgage agencies, only Ginnie Mae carries the full faith and credit of the US government.
✅ Test yourself
Which mortgage-backed security carries the full faith and credit of the U.S. government?
- Freddie Mac MBS
- A private-label CMO
- Fannie Mae MBS
- Ginnie Mae MBS
Answer: D · Ginnie Mae MBS
Ginnie Mae's guarantee is explicitly backed by the full faith and credit of the U.S. government. Fannie Mae and Freddie Mac are GSEs whose guarantees are not, and private-label deals have no government guarantee.
Mortgage rates fall sharply. What risk does a pass-through investor face most?
- Prepayment risk
- Currency risk
- Call protection risk
- Extension risk
Answer: A · Prepayment risk
Falling rates trigger refinancing, so principal comes back early and must be reinvested at lower rates. Extension risk is the rising-rate problem.
The separate classes of a collateralized mortgage obligation are called:
- Strips
- Series
- Tranches
- Pools
Answer: C · Tranches
A CMO divides the cash flows from a mortgage pool into tranches with different payment priorities, maturities and risk. A pool is the underlying mortgages, not the slices.
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