If you have a mortgage, you may be unknowingly participating in a mortgage-backed security (MBS). That is, your humble home loan may be part of a pool of mortgages that has been packaged and sold to income-oriented investors on the secondary market.

Being part of an MBS won’t change much (if anything) about how you repay your home loan, but it’s helpful to understand how these investment products work and how they impact the mortgage and housing industries.

What is a mortgage-backed security?

A mortgage-backed security (MBS) is a type of financial asset, somewhat like a bond (or a bond fund). It’s created out of a portfolio, or collection, of residential mortgages.

When a company or government issues a traditional bond, they are essentially borrowing money from investors (the people buying the bond). As with any loan, interest payments are made and then principal is paid back at maturity. However, with a mortgage-backed security, interest payments to investors come from the thousands of mortgages that underlie the bond — specifically, the repayments in interest and principal the mortgage-holders make each month.

Mortgage-backed securities offer key benefits to the players in the mortgage market, including banks, investors and even mortgage borrowers themselves. However, investing in an MBS has pros and cons.

How do mortgage-backed securities work?

While we all grew up with the idea that banks make loans and then hold those loans until they mature, the reality is that there’s a high chance that your lender is selling the loan into what’s known as the secondary mortgage market. Here, aggregators buy and sell mortgages, finding the right kind of mortgages for the security they want to create and sell on to investors. This is the most common reason a borrower’s mortgage loan servicer changes after securing a mortgage loan.

Mortgage-backed securities consist of a group of mortgages that have been organized and securitized to pay out interest like a bond. MBSs are created by companies called aggregators, including government-sponsored entities such as Fannie Mae or Freddie Mac. They buy loans from lenders, including big banks, and structure them into a mortgage-backed security.

Think of a mortgage-backed security like a giant pie with thousands of mortgages thrown into it. The creators of the MBS may cut this pie into potentially millions of slices — each perhaps with a little piece of each mortgage — to give investors the kind of return and risk they demand. Mortgage-backed securities typically pay out to investors on a monthly basis, like the mortgages underlying them.

Types of mortgage-backed securities

Mortgage-backed securities may have many features depending on what the market demands. The creators of MBSs think of their pool of mortgages as streams of cash flow that might run for 10, 15 or 30 years — the typical length of mortgages. But the bond’s underlying loans may be refinanced, and investors are repaid their principal and lose the cash flow over time.

By thinking of the characteristics of the mortgage as a stream of risks and cash flows, the aggregators can create bonds that have certain levels of risks or other characteristics. These securities can be based on both home mortgages (residential mortgage-backed securities) or on loans to businesses on commercial property (commercial mortgage-backed securities).

There are different types of mortgage-backed securities based on their structure and complexity:

• Pass-through securities: In this type of mortgage-backed security, a trust holds many mortgages and allocates mortgage payments to its various investors depending on what share of the securities they own. This structure is relatively straightforward.
• Collateralized mortgage obligation (CMO): This type of MBS is a legal structure backed by the mortgages it owns, but it has a twist. From a given pool of mortgages, a CMO can create different classes of securities that have different risks and returns (like different size slices, if we use our pie metaphor again). For example, it can create a “safer” class of bonds that are paid before other classes of bonds. The last and riskiest class is paid out only if all the other classes receive their payments.
• Stripped mortgage-backed securities (SMBS): This kind of security basically splits the mortgage payment into two parts, the principal repayment and the interest payment. Investors can then buy either the security paying the principal (which pays out less at the start but grows) or the one paying interest (which pays out more but declines over time). These structures allow investors to invest in mortgage-backed securities with certain risks and rewards. For example, an investor could buy a relatively safe slice of a CMO and have a high chance of being repaid, but at the cost of a lower overall return.

How do mortgage-backed securities affect mortgage rates?

The cost of mortgage-backed securities has a direct impact on residential mortgage rates. This is because mortgage companies lose money when they issue loans while the market is down.

When the prices of mortgage-backed securities drop, mortgage providers generally increase interest rates. Conversely, mortgage providers lower interest rates when the price of MBSs goes up.

So, what causes mortgage-backed securities to rise or fall? Everything from stock market gains to higher energy prices and even unemployment numbers have the ability to influence the prices. A variety of factors that affect the course of mortgage-backed securities, and lenders are constantly monitoring it.

Mortgage-backed securities and the housing market

Why do mortgage-backed securities make sense for the players in the mortgage industry? Mortgage-backed securities actually make the industry more efficient, meaning it’s cheaper for each party to access the market and get its benefits:

• Lenders: By selling their mortgages, lenders save on maintenance costs, and receive money they can then loan out to other borrowers, allowing them to more efficiently use their capital. They often require borrowers to meet conforming loan standards so that they can sell mortgages to aggregators. They can also sell the loans they might not want to keep, while retaining those they prefer.
• Aggregators: Aggregators package mortgages into MBSs and earn fees for doing so. They may give mortgage-backed securities features that appeal to certain investors. A steady supply of conforming loans allows aggregators to structure MBSs cheaply.
• Borrowers: Because aggregators demand so many conforming loans, they increase the supply of these loans and push down mortgage rates. So, borrowers may be able to enjoy greater access to capital and lower mortgage rates than they otherwise would.

Of course, easier access to financing is beneficial for the housing construction industry:  Developers can build and sell more houses to consumers who are able to borrow more cheaply.

Investors like mortgage-backed securities, too, because these bonds may offer certain kinds of risk exposure that the investors, mainly big institutional players, want to have. Even the banks themselves may invest in MBSs, diversifying their portfolios.

While the lender may sell the loan, it may also retain the right to service the mortgage, meaning it earns a small fee for collecting the monthly payment and generally managing the account. So, you may continue to pay your lender each month for your mortgage, but the real owner of your mortgage may be the investors who hold the mortgage-backed security containing your loan.

Pros and cons of investing in MBSs

No investment is without risk. MBS have their advantages and disadvantages.

For instance, mortgage-backed securities typically pay out to investors on a monthly basis, like the mortgages behind the securities. But, unlike a typical bond where you receive interest payments over the bond’s life and then receive your principal when it matures, an MBS may often pay both principal and interest over the life of the security, so there won’t be a lump-sum payment at the end of the MBS’ life.

Here are some of the other advantages and disadvantages of investing in MBSs.

History of mortgage-backed securities

The first modern-day mortgage-backed security was issued in 1970 by the Government National Mortgage Association, better known as Ginnie Mae. These mortgage-backed securities were actually backed by the U.S. government and were enticing because of their guaranteed income stream.

Ginnie Mae began providing mortgage-backed securities in an effort to bring in extra funds, which were then used to purchase more home loans and expand affordable housing. Shortly after, government-sponsored enterprises Fannie Mae and Freddie Mac also began offering their version of MBSs.

The first private MBS was not issued until 1977, when Lew Ranieri of the now-defunct investment group Salomon Brothers developed the first residential MBS that was backed by mortgage providers, rather than a federal agency. Ranieri’s MBSs were offered in 5- and 10-year bonds, which was attractive to investors who could see returns more quickly.

Over the years, mortgage-backed securities have evolved and grown significantly. As of May 2023, financial institutions have issued $493.9 billion in mortgage-backed securities.

Mortgage-backed securities today

While mortgage-backed securities were notoriously at the center of the global financial crisis in 2008 and 2009, they continue to be an important part of the economy today because they serve real needs and provide tangible benefits to players across the mortgage and housing industries.

Not only does securitization of mortgages provide increased liquidity for investors, lenders and borrowers, it also offers a way to support the housing market, which is one of the largest engines of economic growth in the U.S. A strong housing market often bolsters a strong economy and helps employ many workers.