Pass-Through Security
What Is a Pass-Through Security?
A pass-through security is a derivative that represents a direct claim on a pool of debt obligations, such as mortgages, where the principal and interest payments collected from the debtors are passed through to the investors.
A pass-through security is an investment vehicle that pools together various debt obligations—most commonly residential mortgages—and sells shares of that pool to investors. As the underlying borrowers make their monthly payments of principal and interest, those funds are collected by a servicing intermediary and then "passed through" to the investors who hold the securities, minus a servicing fee. This structure allows banks and other lenders to remove loans from their balance sheets, freeing up capital to originate new loans. For investors, pass-through securities offer a way to invest in a diversified portfolio of loans that would be difficult to assemble individually. While mortgage-backed securities (MBS) are the quintessential example, pass-throughs can also be backed by other types of debt, such as auto loans or credit card receivables. The key characteristic is that the cash flows from the collateral flow directly to the investor. The appeal of pass-through securities lies in their regular income streams, which often offer higher yields than Treasury bonds of comparable maturity. However, they introduce unique risks, particularly prepayment risk—the possibility that homeowners will refinance or sell their homes when interest rates fall, returning the principal to the investor sooner than anticipated and forcing reinvestment at lower rates.
Key Takeaways
- Pass-through securities are pools of fixed-income securities backed by a package of assets.
- Investors receive a pro-rata share of the principal and interest payments made by the borrowers in the pool.
- Mortgage-backed securities (MBS) are the most common type of pass-through security.
- These securities carry prepayment risk, as borrowers may pay off their loans earlier than expected.
- The "pass-through" name comes from the way payments from the underlying borrowers are funneled to the investors.
- Ginnie Mae, Fannie Mae, and Freddie Mac are major issuers of mortgage pass-through certificates.
How Pass-Through Securities Work
The creation of a pass-through security begins with a financial institution, such as a bank, originating a large number of loans. Instead of holding these loans to maturity, the institution groups them into a pool based on similar characteristics like maturity date and interest rate. This pool is then sold to a government agency (like Ginnie Mae) or a government-sponsored enterprise (like Fannie Mae or Freddie Mac), or a private financial institution. The securitizing entity issues certificates representing ownership interest in the pool. When the original borrowers make their monthly mortgage payments, a servicer collects the funds. The servicer deducts a fee for administrative costs and a guarantee fee (if applicable) and distributes the remaining funds to the certificate holders. This usually happens on a monthly basis, matching the payment schedule of the underlying loans. Because the payments passed to investors fluctuate based on the actual payments made by borrowers (including prepayments), the monthly cash flow from a pass-through security can vary. If interest rates drop, prepayments typically rise, increasing the principal returned to investors. Conversely, if rates rise, prepayments slow down, extending the duration of the security. This variability makes modeling cash flows more complex than for standard bonds.
Key Elements of Pass-Through Securities
Understanding pass-through securities requires familiarity with several core components that define their structure and performance. First is the Underlying Asset Pool, which consists of thousands of individual loans. The credit quality and characteristics of these loans determine the risk profile of the security. Second is the Servicer, the entity responsible for collecting payments from borrowers, handling delinquencies, and distributing funds to investors. Third is the Pass-Through Rate, which is the interest rate paid to investors. This rate is always lower than the average interest rate on the underlying loans because the servicer and the issuer deduct fees before passing the payments along. Finally, the Prepayment Speed measures how quickly borrowers are paying off the underlying loans, which directly impacts the investor's yield and the security's average life.
Important Considerations for Investors
Investors in pass-through securities must carefully evaluate prepayment risk and extension risk. Prepayment risk occurs when interest rates fall, leading homeowners to refinance. This returns principal to the investor earlier than expected, often compelling them to reinvest in lower-yielding assets. Extension risk is the opposite: when interest rates rise, prepayments slow down, and the investor's capital is tied up for longer than anticipated at a below-market rate. Additionally, while agency-backed pass-throughs (like those from Ginnie Mae) carry an explicit government guarantee, others (like non-agency MBS) carry credit risk, meaning investors could lose money if borrowers default. Liquidity is generally high for agency pass-throughs but can be lower for private-label securities. Taxation is another factor; interest income from pass-throughs is typically fully taxable at the federal, state, and local levels. Investors should also be aware of the "negative convexity" profile of these securities, meaning their price appreciation is capped when rates fall (due to prepayments) but they can fall significantly when rates rise.
Real-World Example: Mortgage-Backed Pass-Through
Imagine an investor purchases a pass-through security backed by a pool of 30-year fixed-rate mortgages with a total face value of $100 million. The weighted average coupon (interest rate) of the mortgages is 6%. The issuer and servicer deduct a total of 0.5% in fees, leaving a pass-through rate of 5.5% for the investor. In the first month, if no borrowers prepay, the investor receives a payment calculated based on the 5.5% annual rate plus the scheduled principal amortization. However, if mortgage rates in the market drop to 4%, many homeowners in the pool might refinance. Consequently, the investor might receive a large lump-sum principal payment in month 12, effectively retiring a portion of the investment early. The investor now has cash back but must find a new place to invest it, likely at the new lower market rate of 4%.
Advantages of Pass-Through Securities
Pass-through securities offer several distinct advantages for income-focused investors. Primarily, they typically provide higher yields than U.S. Treasury bonds of similar maturities, compensating investors for prepayment risk. They also offer regular monthly income, whereas most bonds pay interest semiannually. This can be attractive for retirees or those needing consistent cash flow. Furthermore, agency pass-throughs (Ginnie Mae) are backed by the full faith and credit of the U.S. government, virtually eliminating default risk. Even GSE-backed securities (Fannie Mae, Freddie Mac) are considered to have very high credit quality. Liquidity is another benefit; the market for agency MBS is massive and highly active, making it easy for investors to buy and sell positions without significant price impact.
Disadvantages of Pass-Through Securities
The primary disadvantage is the uncertainty of cash flows caused by prepayment risk. Unlike a standard bond with a fixed maturity date, a pass-through security's life can shorten or lengthen based on interest rate movements. This negative convexity creates a "heads I lose, tails you win" dynamic: when rates fall (and bond prices should rise), pass-throughs appreciate less because of prepayments. When rates rise (and prices fall), pass-throughs may fall more because the duration extends. Additionally, the monthly income payments include both interest and returned principal. Investors who spend the entire monthly check may unknowingly be eroding their principal balance, leaving them with less capital working for them over time.
Pass-Through Security vs. Collateralized Mortgage Obligation (CMO)
While both are backed by pools of mortgages, they structure the risk differently.
| Feature | Pass-Through Security | CMO (Collateralized Mortgage Obligation) |
|---|---|---|
| Structure | Single class of shares; pro-rata distribution | Multiple tranches with different rules |
| Cash Flow | Investors receive pro-rata share of all payments | Directed to specific tranches by priority |
| Prepayment Risk | Shared equally by all investors | Redistributed; some tranches are protected, others absorb it |
| Complexity | Low; simple flow-through structure | High; complex rules for principal distribution |
FAQs
The most common type is the Mortgage-Backed Security (MBS), specifically those issued by Ginnie Mae, Fannie Mae, and Freddie Mac. In these securities, the underlying assets are residential mortgage loans. When homeowners make their monthly mortgage payments, the cash is collected and passed through to the MBS holders. Ginnie Mae pass-throughs are unique because they are backed by the full faith and credit of the U.S. government.
Prepayment risk is the risk that borrowers will pay off their loans earlier than scheduled, typically through refinancing when interest rates decline. For a pass-through investor, this means receiving the principal back sooner than expected. While getting money back sounds good, it usually happens when rates are low, forcing the investor to reinvest that capital into lower-yielding assets. This limits the price appreciation of the security.
Yes, the income generated from pass-through securities is generally fully taxable. The interest portion of the monthly payment is taxed as ordinary income at the federal, state, and local levels. This differs from municipal bonds, which are often tax-exempt, or U.S. Treasuries, which are exempt from state and local taxes. Investors should consult a tax advisor to understand the specific implications for their portfolio.
The main difference lies in the guarantee. Ginnie Mae (GNMA) securities are backed by the full faith and credit of the U.S. government, meaning there is virtually no default risk. Fannie Mae (FNMA) and Freddie Mac (FHLMC) are government-sponsored enterprises (GSEs); their securities carry an implicit, rather than explicit, government guarantee, though they are considered to have very high credit quality. Consequently, Ginnie Maes often trade at slightly lower yields than Fannie or Freddie securities.
Pass-through securities pay monthly because the underlying assets—typically mortgages—are paid monthly by borrowers. As homeowners send in their monthly checks for principal and interest, the servicer collects these funds and distributes them to investors (after deducting fees) on a monthly basis. This matches the cash flow of the underlying collateral, unlike most corporate or government bonds that pay interest semiannually.
The Bottom Line
Investors seeking regular monthly income and yields higher than Treasuries may consider pass-through securities. A pass-through security is a derivative that pools debt obligations, like mortgages, and passes payments from borrowers to investors. Through this mechanism, pass-throughs provide diversification and steady cash flow. On the other hand, they carry significant prepayment risk, meaning the income stream can be unpredictable if interest rates change. For most individual investors, these are best accessed through mutual funds or ETFs to ensure professional management of the complex risks involved. They remain a cornerstone of the U.S. fixed-income market, providing the liquidity that makes affordable housing finance possible.
Related Terms
More in Structured Products
Key Takeaways
- Pass-through securities are pools of fixed-income securities backed by a package of assets.
- Investors receive a pro-rata share of the principal and interest payments made by the borrowers in the pool.
- Mortgage-backed securities (MBS) are the most common type of pass-through security.
- These securities carry prepayment risk, as borrowers may pay off their loans earlier than expected.