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Why Does the Federal Reserve Buy Mortgage-Backed Securities?

When the economy falters, the Federal Reserve has multiple tools to encourage borrowing and spending. While many people know the Fed raises or lowers short-term interest rates, fewer understand why it directly purchases mortgage-backed securities (MBS) — bundles of home loans sold by banks to investors. These purchases represent one of the Fed's most direct interventions in the housing market, yet they remain misunderstood. Understanding Fed MBS purchases helps explain how central banks attempt to restart economies and why housing markets are often in the spotlight during recessions.

Quick definition: The Federal Reserve buys mortgage-backed securities to inject money into the financial system, lower mortgage rates, and encourage home buying when traditional interest-rate cuts can no longer stimulate the economy.

Key takeaways​

  • Fed MBS purchases inject money directly into the housing market by buying loan bundles from banks, freeing up capital for new lending.
  • When short-term interest rates hit zero, the Fed turns to asset purchases (quantitative easing) because cutting rates further becomes impossible.
  • MBS purchases lower mortgage rates by increasing demand for these securities, making it cheaper for banks to originate new home loans.
  • The Fed's balance sheet ballooned from under $1 trillion (2007) to over $7 trillion (2021) due partly to MBS holdings.
  • Housing-market stimulus through MBS purchases can fuel asset inflation and wealth inequality if bond buying outpaces real economic growth.
  • The unwinding (sale or maturation) of MBS holdings has become controversial as the Fed normalizes its balance sheet post-crisis.

What are mortgage-backed securities?​

A mortgage-backed security is a financial instrument created when a bank sells a pool of home mortgages to investors. Instead of holding a mortgage until a borrower pays it off (which can take 30 years), banks package hundreds or thousands of mortgages and sell them. Investors who buy these securities receive monthly payments of principal and interest from homeowners.

For example, Acme Bank originates a $300,000 home loan at 4.5% interest. Rather than wait 30 years to be repaid, the bank sells that loan (along with 2,000 others) to an MBS investor. The investor becomes the effective lender, and homeowners send monthly payments to a loan servicer who distributes cash to the MBS holder.

This system has existed for decades and normally works as a private market: banks originate loans, investment firms (hedge funds, insurance companies, pension funds, other banks) buy the securities. The Federal Reserve, however, has become the largest MBS buyer in history during financial crises.

Why traditional rate cuts don't work in deep recessions​

In normal times, the Fed stimulates the economy by lowering the federal funds rate — the short-term interest rate banks charge each other overnight. When banks can borrow cheaply overnight, they lower mortgage rates, credit-card rates, and business-loan rates to remain competitive. Lower rates encourage borrowing and spending, which theoretically revives growth.

But in severe recessions — like 2008 or 2020 — the Fed cuts rates all the way to zero. Once rates hit zero, the central bank cannot cut them further; this is called the "zero lower bound" or liquidity trap. In 2008, for instance, the Fed had already dropped rates from 5.25% to near zero by December 2008, yet the housing collapse continued, unemployment soared, and banks refused to lend.

At this point, rate cuts alone become powerless. The Fed must find a different tool: quantitative easing (QE), which means buying large quantities of bonds and securities from the open market. By purchasing MBS, the Fed can inject money into the financial system and push longer-term interest rates lower, even when short-term rates are already at zero.

How Fed MBS purchases affect mortgage rates​

When the Federal Reserve announces it will buy $100 billion of mortgage-backed securities, several immediate market effects unfold.

First, demand for MBS surges. If the Fed is willing to pay (say) 99 cents on the dollar for a 3.5% mortgage-backed security, other investors take note. Prices for existing MBS rise, which means yields fall. When prices go up, the coupon yield (the interest payment) becomes a smaller percentage of what you paid — so you earn less on the principal if you buy at that price.

Second, banks holding MBS inventories find ready buyers in the Fed, so they face less pressure to discount those securities to sell them. This encourages banks to continue originating new mortgages rather than hoarding them.

Third, and most importantly, lower MBS prices mean lower mortgage rates for homebuyers. Here's why: when banks originate a new mortgage, they immediately sell it into the MBS market to free up capital and remove interest-rate risk. If the Fed is buying MBS aggressively, banks can sell mortgages easily and at competitive prices. They pass these savings to homebuyers by offering lower rates. A homebuyer who might have faced a 5.5% mortgage rate in a stressed market might instead lock in 3.5% if the Fed is actively buying MBS.

The effect is measurable. Research from the Federal Reserve itself has shown that each $100 billion of Fed MBS purchases lowers 30-year mortgage rates by roughly 10–15 basis points (0.10–0.15 percentage points) in the short term.

The Fed's MBS holdings: scale and timeline​

To understand the magnitude of Fed intervention, consider the numbers.

In June 2007, before the financial crisis, the Fed's total assets were approximately $900 billion, and it held almost no MBS. The Fed's balance sheet was nearly pristine — mostly Treasury bonds held for traditional monetary-policy operations.

By late 2008, as the housing crisis deepened, the Fed began purchasing MBS under an emergency program. Between late 2008 and the peak of QE in 2014, the Fed accumulated roughly $1.75 trillion in MBS holdings. For context, the entire U.S. mortgage market is roughly $12 trillion, so the Fed owned nearly 15% of all MBS at the peak.

The Fed's total balance sheet reached $4.5 trillion by 2015. A significant portion — over $1.3 trillion — was MBS.

During the COVID-19 crisis in March 2020, the Fed restarted MBS purchases, eventually buying an additional $500+ billion in 2020 alone. By January 2021, the Fed's MBS holdings peaked at approximately $2.1 trillion across all vintages, and the total Fed balance sheet exceeded $7 trillion.

This unprecedented expansion of MBS purchases had tangible effects: 30-year mortgage rates fell below 3% in 2020, near historic lows, enabling a housing boom even as the pandemic killed jobs and economic activity plummeted.

Real-world examples​

The 2008–2009 financial crisis: After Lehman Brothers collapsed in September 2008, panic swept through financial markets. The commercial paper market froze, and banks stopped lending to each other and to borrowers. The Fed, having already cut short-term rates to zero, announced in November 2008 that it would purchase up to $500 billion in MBS. This was shocking — the Fed had never done this at scale before. The policy signaled the Fed would backstop the housing market and ensure mortgage credit remained available. By mid-2009, as MBS purchases continued, mortgage rates stabilized around 5%, down from panic highs above 6.5%, and housing-market stabilization gradually began. The program expanded to $1.75 trillion total. For details on the Fed's crisis response, see the Federal Reserve's official history.

The 2012 operation twist: By mid-2012, the Fed had already purchased huge quantities of MBS, but mortgage rates remained sticky above 3.5%, and the housing recovery was sluggish. The Fed announced it would extend the maturity of its MBS holdings and concentrate purchases in longer-duration securities to exert even more downward pressure on mortgage rates. By late 2012, mortgage rates had fallen below 3.3%, and the housing market began recovering more decisively. Home sales in 2012–2013 rose 15–20% year-over-year.

The 2020–2021 pandemic response: On March 23, 2020, as COVID-19 spread and stock markets plunged, the Fed announced it would purchase "unlimited" amounts of MBS and Treasuries. This "shock and awe" approach calmed markets immediately. By May 2020, despite unemployment hitting 14.7%, mortgage rates had fallen to 2.9–3.1%, the lowest on record. Homebuyers rushed to lock in these rates, and the U.S. experienced a surprise housing boom in 2020–2021, with median home prices rising 20%+ year-over-year in many markets. The Fed's MBS purchases were a critical enabler. See the Federal Reserve's monetary policy page for contemporary press releases.

Common mistakes​

Mistake 1: Confusing Fed MBS purchases with the Fed printing money. Some people believe the Fed literally prints new physical currency to buy MBS. In reality, the Fed creates electronic bank reserves (digital money in bank accounts at the Fed) when it purchases MBS. These reserves allow banks to lend, but the money supply doesn't explode overnight — it expands gradually as banks deploy those reserves into the real economy through new loans and investments.

Mistake 2: Assuming MBS purchases always lower mortgage rates. Fed MBS purchases do push mortgage rates lower all else equal, but market expectations matter greatly. If investors believe future inflation will be very high, longer-term rates may rise even as the Fed buys MBS, overwhelming the downward pressure. During 2021–2022, despite the Fed still holding a large MBS portfolio, mortgage rates rose sharply as inflation fears grew.

Mistake 3: Believing the Fed's MBS purchases are risk-free. When the Fed purchases MBS during a crisis, it accepts significant interest-rate risk and extension risk (the risk that homeowners won't refinance when rates fall, locking the Fed into below-market yields for years). If rates rise sharply after the Fed has bought heavily, the market value of those MBS holdings can fall substantially. The Fed faces "paper losses" on its balance sheet, which can become politically contentious.

Mistake 4: Ignoring the lag between Fed purchases and housing-market response. Mortgage rates can fall within days of Fed announcement, but it takes weeks or months for homebuyers to refinance or purchase new homes, and for banks to fully adjust lending behavior. Policymakers sometimes become impatient and expand MBS purchases further before the earlier round has taken full effect.

Mistake 5: Assuming all MBS securities are equally risky. The Fed primarily purchases agency MBS — securities implicitly guaranteed by government-sponsored enterprises like Fannie Mae and Freddie Mac. These carry minimal credit risk (nearly zero default risk on principal). Non-agency MBS, created from subprime or jumbo mortgages without government backing, are far riskier. The Fed has historically avoided non-agency MBS, but during the 2008 crisis it did purchase some, accepting higher risk in the process.

FAQ​

Q: Does the Fed make money or lose money when it buys MBS?

A: The Fed's MBS purchases are not profit-seeking transactions; they are policy tools. However, the Fed does earn returns. When it buys a 3% MBS security, it receives 3% annual interest on that investment. The Fed remits its profits to the U.S. Treasury, so in a sense, taxpayers benefit. However, if the Fed buys MBS when rates are high and rates later fall, the Fed's holdings are underwater on a mark-to-market basis, though the Fed typically holds them to maturity and doesn't realize losses.

Q: Can the Fed buy individual mortgages directly from homeowners?

A: No. The Fed only purchases MBS — pre-made packages of mortgages — from financial institutions. It doesn't originate loans or interact directly with borrowers. This preserves the Fed's role as a monetary-policy tool rather than a lender of last resort to consumers.

Q: What happens to MBS after the Fed buys them?

A: The Fed holds them and collects monthly principal and interest payments as homeowners pay down their mortgages. As mortgages mature (typically over 30 years), the Fed's MBS holdings naturally decline. The Fed can also sell MBS if it chooses, though it has historically preferred to let them run off rather than sell them actively.

Q: When does the Fed stop buying MBS?

A: The Fed decides based on economic conditions. It typically stops buying and begins planning to "unwind" its balance sheet when unemployment falls and inflation is under control. In late 2021, the Fed announced it would taper MBS purchases and begin allowing MBS holdings to mature without replacement in early 2022. In 2023–2024, as the Fed fought inflation by raising rates, it allowed its MBS portfolio to shrink passively.

Q: Does Fed MBS buying cause house prices to rise?

A: Fed MBS purchases lower mortgage rates, which increases homebuying demand and can push house prices higher. However, the mechanism is indirect — lower rates don't directly raise prices, but they increase the number of buyers who can afford homes. If housing supply is constrained (as it often is), increased demand can indeed drive prices up. This is a source of criticism: some argue Fed MBS purchases fuel unaffordable housing and wealth inequality.

Q: Do other central banks buy MBS?

A: Very few. The U.S. has the deepest, most liquid MBS market globally, and Fannie Mae/Freddie Mac's guarantees make agency MBS unique. Other central banks like the ECB or Bank of Japan focus on buying government bonds (sovereigns) rather than MBS. However, after the COVID-19 shock, some central banks did explore MBS or mortgage-loan purchases as alternative tools.

The Fed's MBS purchases are interconnected with broader monetary-policy strategies. Understanding them requires familiarity with quantitative easing, the larger asset-purchase program of which MBS purchases are a part. The impact of lower mortgage rates is closely tied to how the Fed sets interest rates and the mechanics of the transmission mechanism. Fed MBS holdings also interact with inflation expectations — when investors believe future inflation is high, longer-term rates rise regardless of Fed buying, as seen in 2021–2022. Additionally, the Fed's MBS strategy reflects lessons from the 2008 financial crisis, when traditional monetary policy proved insufficient. Finally, the debate over whether MBS purchases are inflationary or deflationary connects to broader discussions about inflation and central banks' role.

Summary​

The Federal Reserve purchases mortgage-backed securities to lower borrowing costs and stimulate housing markets when short-term interest rates have already fallen to zero. By buying MBS, the Fed injects money into the financial system, increases demand for these securities (lowering their yields), and enables banks to originate new mortgages at lower rates. The scale of Fed MBS purchases has been enormous — from negligible in 2007 to over $2 trillion by 2021 — making the Fed the largest holder of these securities globally. While MBS purchases have successfully lowered mortgage rates during crises (2008–2009 and 2020), they are not without controversy, as they may fuel asset-price inflation and wealth inequality if pursued for extended periods. Understanding why the Fed buys MBS illuminates how central banks attempt to revive economies when traditional policy tools have been exhausted.

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