Reviewed by Cierra Murry
Despite their infamous reputation for their role in the financial crisis of 2007-2008, there are several different arguments in favor of allowing market participants to trade and own mortgage-backed securities (MBS).
At its basic level, an MBS is any investment solution that uses commercial or residential mortgage or a pool of mortgages as the underlying asset. Like most financial innovations, the purpose of an MBS is to increase return and diversify risk. By securitizing pools of similar mortgages, investors can absorb the statistical likelihood of non-payment.
However, an MBS is a complicated instrument and comes in many different forms. It would be difficult to asses the general risk of an MBS, much like it would be difficult to assess the risk of a generic bond or stock. The nature of the underlying asset and the investment contract are large determinants of risk.
Advisor Insight
- Mortgage-backed securities(MBS) are tradeable securities backed by the cash flow from a portfolio of mortgages.
- In theory, MBS diversify risk by providing access to a broad portfolio of mortgage debt.
- Mortgage-backed securities played a key role in the 2008 financial crisis when many of the underlying loans defaulted.
- Today, mortgage-backed securities are still popular among investors seeking diversified exposure to real estate lending.
Improved Liquidity and Risk Argument
Mortgage debt and pools of mortgages are sold by financial institutions to individual investors, other financial institutions and governments. The money received is used to offer other borrowers loans, including subsidized loans for low-income or at-risk borrowers. In this way, an MBS is a liquid product.
Mortgage-backed securities also reduce risk to the bank. Whenever a bank makes a mortgage loan, it assumes risk of non-payment (default). If it sells the loan, it can transfer risk to the buyer, which is normally an investment bank. The investment bank understands that some mortgages are going to default, so it packages like mortgages into pools. This is similar to how mutual funds operate. In exchange for this risk, investors receive interest payments on the mortgage debt.
Suggesting that these types of MBS are too risky is an argument that could apply to any type of securitization, including bonds and mutual funds.
Aggregate Arguments: Consumption Smoothing and More Homes
Economic research has suggested that, in both domestic and international markets, the securitization of the mortgage market has led to the sharing of consumption risk. This allows banking institutions to supply credit even during downturns, smoothing out the business cycle and helping normalize interest rates among different populations and risk profiles. Theoretically, the level of consumer spending in the market is smoother and less prone to recession/expansion fluctuations as a result of increased securitization.
The unquestioned result of mortgage securitization has been an increase in home ownership and a reduction in interest rates. Through the MBS and its derivative, the collateralized mortgage obligation, banks have been more able to provide home credit to borrowers who otherwise would have been priced out of the market.
$1.59 trillion
The total value of mortgage-backed securities issued in the U.S. in 2024.
Federal Reserve Involvement
While the MBS market draws a number of negative connotations, the market is more “safe” from an individual investment stand point than it was pre 2008. After the collapse of the housing market, and on the back of strict regulation, banks increased the underwriting standards and made their loans more robust and transparent.
The Federal Reserve remains a big player in the MBS market. As of Feb. 2025, the Fed’s balance sheet included $2.2 trillion in MBS. With the central bank a significant player, the MBS market has clawed back much of its credibility.
Free to Contract Argument
There is another argument in favor of allowing MBS that has less to do with financial arguments and more to do with the nature of capitalism itself: Capitalism is a profit and loss system, built on the argument that voluntary exchange and individual determination are ultimately preferable to government restrictions. Nobody coerces a borrower into taking out a mortgage loan, just as no financial institution is legally obligated to make additional loans and no investor is forced to purchase an MBS.
The MBS allows investors to seek a return, lets banks reduce risk and gives borrowers the chance to buy homes through free contracts.
What Are the Risks of Mortgage-Backed Securities?
There are three main risks for investors in mortgage-backed securities: interest rate risk, prepayment risk, and default risk. Interest rate risk refers to the chance that market-wide interest rates will increase, thereby reducing the market value of existing contracts. This is common to all fixed-income investments, not just MBS. Prepayment risk is the possibility that some borrowers will pay off their loans early, thereby reducing the total income for MBS holders. Default risk is the possibility that a large number of borrowers will default, thereby reducing the investors’ income stream.
How Did Mortgage-Backed Securities Contribute to the Financial Crisis?
Prior to the 2008 financial crisis, many banks and lenders chose to securitize their mortgage assets and sell them, rather than keep those loans on their own balance sheets. As the housing bubble inflated, lenders began to lower their lending standards, and used mortgage-backed securities as a convenient way to dispose of high-risk loans. When borrowers started to default, MBS investors were left with underperforming assets.
How Big Is the Market for Mortgage-Backed Securities?
The market for mortgage-backed securities is significant. In 2024, nearly $1.6 trillion of mortgage-backed securities was issued in the United States. The largest component was Agency MBS, issued by government-affiliated bodies like Ginnie Mae.
The Bottom Line
Although mortgage-backed securities(MBS) are commonly associated with the 2008 housing crash, they are still a popular choice for institutional investors. By bundling together a large number of loans, these securities provide investors with broad exposure to a large portfolio of loans, rather than betting on the solvency of a single borrower. Moreover, they also have the effect of smoothing out regional and demographic variations in mortgage interest rates.