Asset Backed Securities (RMBS, CMBS, CDOs)

Updated on April 4, 2024
Article byWallstreetmojo Team
Edited byWallstreetmojo Team
Reviewed byDheeraj Vaidya, CFA, FRM

What Are Asset-Backed Securities? 

Post the global financial crisis of 2008, there was a huge buzz about some sophisticated financial securities known as CDOs, CMBS, & RMBS, and how they played a big role in the build-up of the crisis. These securities are known as Asset-backed Securities (ABS), an umbrella term used to refer to a kind of security that derives its value from a pool of assets, which could be a bond, home loan, car loan, or even credit card payments.


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ABS allows investors to gain exposure to a diversified pool of underlying assets, reducing risk. They also enhance liquidity in financial markets by creating tradable securities backed by various types of assets. However, asset backed securities fund structures can be complex, making it challenging for investors to understand their risks fully.

Key Takeaways

  • Asset-backed securities (ABS) are financial instruments representing claims on underlying assets like mortgages, auto loans, or credit card receivables. These assets are bundled together and sold as securities, allowing investors to gain exposure to the cash flows generated by the underlying assets. 
  • The creation of ABS involves securitization, a process where individual loans or assets are pooled and transferred to a special purpose vehicle (SPV). 
  • ABS manages risk and enhances credit quality through over-collateralization, reserves, and third-party credit enhancements.

Asset-Backed Securities Explained

The creation of ABS provides an opportunity for large institutional investors to invest in higher-yielding asset classesAsset ClassesAssets are classified into various classes based on their type, purpose, or the basis of return or markets. Fixed assets, equity (equity investments, equity-linked savings schemes), real estate, commodities (gold, silver, bronze), cash and cash equivalents, derivatives (equity, bonds, debt), and alternative investments such as hedge funds and bitcoins are more without taking much additional risk, and at the same time, helps lenders in raising capital without accessing primary markets. It also allows the banks to remove the loans from their books as the credit risk for the loans gets transferred to the investors.

The process of pooling of financial assetsFinancial AssetsFinancial assets are investment assets whose value derives from a contractual claim on what they represent. These are liquid assets because the economic resources or ownership can be converted into a valuable asset such as more so that they could be sold to the investors later is called Securitization(we’ll take a deeper look into the process in the later section using examples), done usually by Investment Banks. In the process, the lender sells its portfolio of loans to an Investment Bank, which then repackages these loans as a Mortgage-Backed Security (MBS) and then sells it off to other investors after keeping some commission for themselves.

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Let us understand the different types of ABS in the asset backed securities market through the discussion below.

There are certain overlaps in these instruments as the basic principle of Securitization broadly remains the same while the underlying asset might differ.

Let’s take a look at the different types of Asset-backed Securities:

RMBS (Residential Mortgage-Backed Securities)

Structure of RMBS

Let’s have a look at the structure of RMBS and how they are created:

  1. Consider a bank that gives out home mortgages and has lent out $1bn worth of total loans distributed among thousands of borrowers. The bank will receive repayments from these loans after 5-20 years, depending on the tenure of the loans outstanding.
  2. Now to lend out more loans, the bank will need more capital, which can be raised in several ways, including secured/unsecured bondBondBonds refer to the debt instruments issued by governments or corporations to acquire investors’ funds for a certain more issuance or equity issuance. Another way the bank can raise capital is by selling the loan portfolio or a part of it to a securitization agency like the Federal National Mortgage Association (FNMA), commonly known as Fannie Mae. Due to their stringent requirements, the loans bought by Fannie Mae need to conform to high standards(Unlike the non-agency RMBS issued by private institutions, which are very similar to CDOs).
  3. Now Fannie Mae pools these loans based on their tenures and repackages them as RMBS. Since these RMBS are guaranteed by Fannie Mae (Which is a Government-backed agency), they are given a high credit rating of AAA and AA. Because of high ratings of these securities, risk-averse investorsRisk-averse InvestorsThe term "risk-averse" refers to a person's unwillingness to take risks. Investors who prefer a low-return investment with known risks to a higher-return investment with unknown risks, for example, are more like large Insurance firms and Pension funds are the major investors in such securities.

We’ll look at an example to get a better understanding of RMBS:

RMBS (Residential Mortgage-Backed Securities) Example

Let’s say a bank has 1000 outstanding residential loans worth $1m, each with a maturity of 10 years. Thus the total loan portfolio of banks is $1bn. For ease of understanding, we’ll assume the rate of interest on all these loans is the same at 10%, and the cash flow is similar to a bond wherein the borrower makes annual interest payments every year and pays the principal amount at the end.

  • Fannie Mae purchases the loans from the bank for $1bn(the bank might charge some fees in addition).
  • annual cash flow from loans would be 10% * 1bn = $100mn
  • cashflow in 10th year = $1.1bn
  • assuming Fannie Mae sells 1000 units of RMBS to investors worth $1mn each
  • After incorporating the fees of 2% charged by Fannie Mae for taking the credit risk, the yield for investors would be 8%.

Though the yield might not seem to be very high, considering the high credit rating and the yields provided by investment securitiesInvestment SecuritiesInvestment securities are purchased by investors, with or without the assistance of a middleman or agent, solely for the purpose of investment and long-term holding. These are recorded in the financial statements as non-current investments and comprise fixed income and variable income bearing more with similar credit ratings being 1-2% lower. It makes them a very attractive investment option for low-risk investors like Insurance firms and pension funds.

The risk associated with RMBS comes into play when the borrowers start defaulting on their mortgages. A small number of defaults, say 10 out of 1000, will not make much of a difference from the investor’s point of view, but when a large number of borrowers default at the same time, it becomes an issue for investors as the yield generated gets significantly impacted.

CMBS (Commercial Mortgage-Backed Securities)

Structure of CMBS

Let’s have a look at the structure of CMBS and how they are created:

  1. Consider a bank that gives out commercial mortgages for properties such as apartment complexes, factories, hotels, warehouses, office buildings, and shopping malls. And has lent out a certain sum of money for various durations across a diversified set of borrowers for commercial purposes.
  2. Now the bank will sell its commercial mortgage loan portfolio to a securitization agency like Fannie Mae (as we saw with RMBS), which then bundles these loans into a pool and then creates a series of bonds out of these termed various tranches.
  3. These tranches are created based on the quality of loans and the risk associated with them. The senior tranches will have the highest payment priority, would be backed by high-quality shorter duration (As the risk associated is lower) loans, and will have lower yields. While the junior tranches will have lower payment priority, they would be backed by longer-term loans and will have higher yields.
  4. These tranches are then assessed by rating agencies and assigned ratings. The senior tranches will have higher credit ratings falling within the Investment gradeInvestment GradeInvestment grade is the credit rating of fixed-income bonds, bills, and notes as assigned by the credit rating agencies like Standard and Poor’s (S&P), Fitch, and Moody’s to express the creditworthiness of and risk associated with these more (rating above BBB-) category while the junior tranches with lower ratings will fall within the High yield (BB+ and below) category.
  5. This gives investors the flexibility to choose the type of CMBS security based on their risk profile. Large institutional investors with a low-risk profile would prefer to invest in senior-most tranches (rated AA & AAA), while risky investors like hedge fundsHedge FundsA hedge fund is an aggressively invested portfolio made through pooling of various investors and institutional investor’s fund. It supports various assets providing high returns in exchange for higher risk through multiple risk management and hedging more and trading firms might prefer lower-rated bonds due to higher returns.

CDOs (Collateralized Debt Obligations)

asset backed securities
  • The tranches are assigned credit ratings by rating agencies based on the risk they carry.
  • The senior tranche is assigned the highest rating of AAA as they carry the lowest risk though with lower yields. The middle tranches with a moderate risk-rated between AA to BB are known as a Mezzanine tranche.
  • The bottom tranche, which has the lowest rating (in financial parlance, Junk rating) or is unrated, is termed as Equity tranche, and they carry the highest risk as well as higher expected yield.
  • In case the loans in the pool start defaulting, the equity tranche will be the first to take losses while the senior tranche might remain unaffected.
  • An interesting aspect of CDOs is that they can be created out of any fixed-income asset, which could even be other CDOs.
  • For example, it is possible to create a new CDO by pooling sub-prime mortgages or equity tranches of numerous other CDOs (which are basically junk-rated) and then creating a senior tranche from this CDO, which will have a substantially higher rating compared to the underlying assetUnderlying AssetUnderlying assets are the actual financial assets on which the financial derivatives rely. Thus, any change in the value of a derivative reflects the price fluctuation of its underlying asset. Such assets comprise stocks, commodities, market indices, bonds, currencies and interest more (Actual process is a lot more complicated but the basic idea remains same).
  • This was a common practice during the pre-financial crisis years and had a major role in the creation of the asset bubble.
  • The subprime mortgages, in a way, became fuel for the creation of such securities and were being disbursed to anyone and everyone without requisite due diligence.

CDO Example

Let’s look at an example to get a better understanding of CDOs:

Consider a bank that has 1000 outstanding loans (including residential and commercial) worth $1m, each with a maturity of 10 years. Thus the total loan portfolio of a bank is $1bn. For ease of understanding, we’ll assume the rate of interest on all these loans is the same at 10%, and the cash flow is similar to a bond wherein the borrower makes annual interest payments every year and pays the principal amount at the end.

  • An investment bank purchases the loans from the bank for $1bn(the bank might charge some fees in addition).
  • annual cash flow from loans would be 10% x 1bn = $100mn
  • cashflow in 10th year = $1.1bn
  • Now, assuming the investment bank pools these loan assets and repackages them into three tranches: 300,000 units of the senior tranche, 400,000 units of the mezzanine tranche, and 300,000 units of equity tranche worth $1000 each.

Also, for the ease of calculation for the example, we’ll assume that investment bank will include their commission fees in the cost

  • Since the risk for the Senior tranche is lowest, let’s say the coupon arrived at for them is $70 per unit. Resulting in a yield of 7% for them
  • For the Mezzanine tranche, considering the coupon amount arrived at is $90 per unit, giving them a 9% yield
  • Now for the Equity tranche, the coupon amount will be the remaining sum left after paying off Senior and Mezzanine
  • So, total pay-off to Senior tranche = $70 x 300,000 = $21mn
  • total pay-off to Mezzanine tranche = $90 x 400,000 = $36mn
  • Thus, the remaining amount for Equity tranche will be $100mn – ($21mn + $36mn) = $43mn
  • Per unit coupon pay-off comes out to be = $43mn/300k = $143.3
  • Thus giving the equity tranche holders a yield of 14.3%

That looks very attractive compared to other tranches! But remember, here we’ve considered that all the borrowers paid their payments and there was 0% default on payments

  • Now let’s consider the case wherein due to market crash or economic slowdown, thousands of people lost their jobs and now aren’t able to pay the interest payment on their loans.
  • Let’s say this results in 15% of borrowers default on their interest payments.
  • Thus, instead of total cash flow being $100mn, it comes out to be $85mn
  • The whole loss of $15mn will be taken by Equity tranche, leaving them with $28mn. This will result in a per-unit coupon of $93.3 and a yield of 9.3%, almost the same as a mezzanine tranche.

This highlights the risk attached to the lower tranches. In case the default was 40%, the entire coupon payment of the Equity tranche would’ve been wiped out.


The risks in the asset backed securities fund can be split into four main types- credit risk, prepayment risk, market risk, and structural risk. Let us understand each of them in detail through the explanation below.

Credit Risk

  • Asset-backed securities (ABS) are subject to credit risk, which arises from the possibility of default by the underlying assets, such as mortgages, auto loans, or credit card debt.
  • If borrowers default on their payments, the cash flows supporting the ABS may be impaired, leading to losses for investors.

Prepayment Risk

  • ABS backed by assets with prepayment options, such as mortgages or auto loans, face prepayment risk.
  • Rapid prepayments can reduce the expected cash flows and returns on the ABS, negatively impacting investor returns.

Market Risk

  • ABS is also exposed to market risk, including interest rate risk and liquidity risk.
  • Changes in interest rates or market conditions can affect the value of ABS, making them more or less attractive to investors.

Structural Risk

  • The structure of ABS, including the priority of payment to different tranches, can affect the risk profile.
  • Subordination of junior tranches to senior tranches may increase the risk of loss for investors in the junior tranches in the event of defaults.

Frequently Asked Questions (FAQs)

 1. What are the benefits of investing in ABS?

Investing in ABS can provide several advantages, including potential yield enhancements, portfolio diversification, access to specific asset classes, and customizing risk and return profiles.

2. How do ABS differ from traditional bonds?

ABS differ from traditional bonds in that they are backed by specific assets rather than relying solely on the issuer’s creditworthiness. The returns to ABS investors are determined by the cash flows generated by the underlying assets, while traditional bonds depend on the issuer’s ability to make interest and principal payments.

3. What factors should be considered when evaluating ABS?

When evaluating ABS, it is important to consider factors such as the credit quality of the underlying assets, the structure and quality of credit enhancements, the performance of the securitization process, prepayment risks, and the overall economic environment. These factors can significantly impact the risk and potential returns of investing in ABS.

Reader Interactions


  1. ARINJAY says

    Dheeraj Sir,

    This is a great update for us !

    You have been sharing, spreading and propagating knowledge for a long time. Please update the Complete (25-40 slides) formation of a PitchBook (with resources; like which type of information abstracted from which resources (Google, company-website, Database, others et cetra)).

    Around 4- years back i observed a link (of PitchBook) in your course material, but now that is disappeared.

    I/We will wait for your charismatic update.


    • Dheeraj Vaidya says

      Sure Arinjay! Will try.

      p.s. I did receive your email on this too. thanks :-)

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