Have you noticed how mortgage rates have climbed back near multi-year highs while most existing homeowners remain locked into much lower payments? That simple reality has quietly reshaped the risk profile of one of the largest fixed-income markets on the planet. I’ve been watching agency mortgage backed securities more closely this year, and the setup looks different from the painful stretch many investors lived through in 2022 and 2023.
Why Mortgage Backed Securities Deserve Fresh Attention Right Now
Agency mortgage backed securities sit at an interesting crossroads. They still offer a yield pickup over comparable Treasuries and carry essentially no credit risk because of the government-sponsored enterprise guarantee. At the same time, the feature that hurt holders most during the sharp rate rise has largely exhausted itself. Refinancing has dried up. Duration has already extended. Further rate increases would not stretch cash-flow timing the way they once did.
That does not make these securities risk-free. Falling rates can still create a double impact through faster prepayments and shortened duration. Yet even that downside looks more contained today because so many outstanding loans sit well below current market rates. In my view, the balance of risks has improved enough that these bonds merit a place in many fixed-income allocations again.
How Prepayment Behavior Shapes Everything
Mortgage borrowers can repay their loans early without penalty. That option belongs to the homeowner, which means the investor who owns the mortgage backed security is effectively short a call option. The extra yield compensates for that embedded option. When rates drop sharply, borrowers refinance and principal returns early, forcing reinvestment at lower yields. When rates rise, refinancing slows and cash flows stretch further into the future.
The result is negative convexity. Duration lengthens precisely when prices are falling and shortens when prices would otherwise rise most. For years this characteristic created headaches whenever the rate path surprised the market. The last two years delivered a textbook demonstration of extension risk in action.
Today the picture has changed. Nearly four out of five existing mortgages carry rates below 6 percent while the average new 30-year loan sits above 7 percent. Most borrowers have little economic reason to refinance. Prepayment speeds have slowed to levels driven mainly by housing turnover, scheduled amortization, and the occasional default that still returns principal at par for agency securities.
When a mortgage pool sits deeply out of the money, further rate increases produce very little additional extension. The duration that once moved sharply is now relatively stable.
That stability matters. Investors buying agency mortgage backed securities at current levels take on duration that is largely capped on the upside. The painful extension phase has already occurred.
Duration Dynamics in Plain Language
Duration measures how much a bond’s price moves for a given change in yields. A seven-year duration bond typically loses about 7 percent if yields rise one percentage point and gains roughly the same amount if yields fall. For Treasuries and most corporate bonds the number stays relatively predictable because cash flows are fixed. Mortgage backed securities behave differently.
Effective duration for these securities relies on models that estimate how prepayments will respond to rate moves. When rates climb, expected life lengthens and duration rises. When rates fall, expected life shortens and duration falls. The sensitivity is strongest when mortgage rates hover near the coupons of outstanding loans. Once those loans move far out of the money, the relationship flattens.
I’ve found it helpful to think of current conditions as sitting on the flatter part of that curve. Most of the extension risk that investors feared has already been realized. Further increases would still affect prices through higher discount rates, yet the additional duration lengthening should remain modest compared with earlier episodes.
What Happens If Rates Fall Instead
The flip side cannot be ignored. If mortgage rates drop meaningfully, higher-coupon pools face two simultaneous headwinds. Principal returns earlier and must be reinvested at lower yields. At the same time duration shortens, limiting the price appreciation that a parallel Treasury would enjoy.
That double impact is the cost of the prepayment option investors effectively sold. Yet the current distribution of outstanding rates softens the blow. Even a decline of nearly two and a half percentage points would leave the majority of existing mortgages without a strong financial incentive to refinance. Many borrowers simply never act even when the math works in their favor. Credit constraints, small loan balances, or simple inertia keep a portion of the higher coupons alive longer than models sometimes assume.
Housing turnover also plays a constructive role. Lower rates tend to encourage more home sales. Every sale pays off the existing mortgage at par. For securities trading below par, those early returns of principal become realized gains pulled forward in time. The net effect can still prove positive for holders even as some refinancing occurs.
Perhaps the most interesting aspect is the time lag. Borrowers need months to notice lower rates, shop for new loans, and close. Lender capacity can also become constrained after long periods of low activity. These frictions further mute the speed of any prepayment wave.
Practical Ways Individual Investors Can Participate
Owning individual mortgage pools sounds appealing in theory. An investor can select specific coupons, vintages, and geographic concentrations that match a particular view. In practice the market is less friendly to smaller accounts. Pools factor down over time as principal returns, leaving odd-lot positions that trade at discounts. Monthly cash flows arrive in irregular amounts that are hard to reinvest efficiently. Prepayment analysis requires data and models most individuals lack. Dealer access and pricing transparency remain limited for retail-sized trades.
For these reasons most individual investors turn to funds. Passive exchange-traded funds tracking broad agency indexes provide low-cost, diversified exposure. They handle the reinvestment process, maintain balances across coupons and vintages, and benefit from institutional trading advantages. Active funds can tilt toward specific coupons or specified pools that managers believe offer better convexity characteristics, though they charge higher fees for that flexibility.
Anyone considering these vehicles should examine a few key characteristics. Coupon distribution matters because it influences how sensitive the portfolio will be to future rate moves. Effective duration gives a snapshot of current interest-rate exposure. Leverage or derivative use can amplify both gains and losses and should be understood clearly. Two funds with similar stated durations can still behave quite differently depending on the underlying mix of securities.
- Review the weighted average coupon relative to current mortgage rates
- Compare effective duration with that of intermediate Treasuries
- Check expense ratios and any use of leverage or derivatives
- Understand the historical prepayment behavior of the holdings
- Confirm the fund focuses on agency rather than non-agency securities
Balancing the Current Risk and Reward
Three years ago extension risk provided a solid reason to underweight or avoid agency mortgage backed securities. Today that same characteristic has largely run its course and can even serve as a reason to own them. Duration is relatively stable. Credit risk remains minimal. Yields sit at attractive levels compared with Treasuries of similar maturity.
If rates stabilize or begin to decline, holders stand to benefit from both the income stream and potential price appreciation that is less constrained by rapid prepayments than in prior cycles. If rates continue higher, the price impact should more closely resemble that of a conventional intermediate bond rather than the amplified losses seen during the earlier extension phase.
Spreads between mortgage yields and Treasury yields also play a role. They can widen or tighten independently of the overall rate level. At present the combination of limited extension risk and decent spread levels creates a more balanced profile than many fixed-income alternatives.
I’ve found that investors who treat these securities as a core allocation rather than a short-term trade tend to navigate the inevitable volatility more successfully. The income arrives monthly. The government-related guarantee provides comfort during periods of market stress. And the current positioning of outstanding mortgage rates has removed one of the more unpredictable sources of risk.
Key Factors That Will Drive Future Returns
Several variables will determine how these securities perform from here. The path of mortgage rates remains the most important. Housing market turnover affects prepayment speeds even when rates stay elevated. Changes in the supply of new mortgage issuance can influence spreads. Broader demand from banks, money managers, and foreign investors also shifts pricing over time.
One underappreciated element is the seasoning of the existing mortgage universe. Loans originated several years ago now sit far from the refinancing window. Newer production carries higher coupons and will behave differently if rates fall. A diversified portfolio holds both, which helps smooth the overall experience.
Another consideration is the shape of the yield curve. Mortgage rates typically track intermediate Treasuries more closely than the short end. A steepening or flattening curve can alter the attractiveness of the sector relative to other fixed-income choices.
Comparing Mortgage Backed Securities With Other Fixed-Income Options
Treasuries offer unmatched liquidity and pure interest-rate exposure without the prepayment complication. Corporate bonds introduce credit risk and often tighter spreads after accounting for that risk. Municipal bonds appeal mainly to taxable accounts in higher brackets. Agency mortgage backed securities occupy a middle ground: higher yield than Treasuries, minimal credit risk, and a unique cash-flow profile shaped by homeowner behavior.
For investors seeking income without taking significant credit exposure, the sector continues to stand out. The current environment simply makes the risk characteristics more predictable than they have been in several years.
| Characteristic | Agency MBS | Treasuries | Investment-Grade Corporates |
| Credit Risk | Minimal | None | Present |
| Yield Pickup | Meaningful | Baseline | Variable |
| Duration Stability | Improved currently | High | High |
| Prepayment Sensitivity | Present but muted | None | None |
| Liquidity | Strong | Highest | Good |
The table above simplifies a more nuanced comparison, yet it highlights why many portfolios include a dedicated allocation to the sector even after the difficult period of rising rates.
Common Misconceptions Worth Clearing Up
Some investors still associate mortgage backed securities with the financial crisis of more than a decade and a half ago. That episode involved non-agency securities packed with poorly underwritten loans. Agency securities carried government-sponsored enterprise guarantees then and continue to do so today. The distinction remains important.
Another misconception is that these bonds always suffer when rates fall. While negative convexity is real, the severity depends heavily on how far existing coupons sit from current market rates. The present distribution creates a wider buffer than existed in many earlier cycles.
A third point of confusion involves liquidity. The agency market ranks among the deepest and most liquid fixed-income markets globally. Institutional trading occurs in large size with tight bid-ask spreads under normal conditions. Fund vehicles further improve accessibility for smaller accounts.
Building a Thoughtful Allocation
How much of a fixed-income portfolio should sit in agency mortgage backed securities? The answer depends on overall risk tolerance, time horizon, and the rest of the holdings. Many balanced approaches treat the sector as a core intermediate-duration allocation that complements Treasuries and high-quality corporates.
Rebalancing matters. Price movements and principal returns can shift weights over time. Periodic reviews of coupon mix and effective duration help keep the exposure aligned with the original intent. Taxable accounts should also consider the monthly cash-flow pattern and any premium amortization rules that apply.
In my experience, investors who focus on the long-term income characteristics rather than short-term price swings tend to stay more comfortable through the inevitable periods of volatility. The current environment simply offers a more favorable starting point than existed when rates were rising rapidly and duration was still extending.
Looking Ahead With Clear Eyes
No one knows the exact path of interest rates from here. What has become clearer is the limited room left for further harmful duration extension. That single change improves the risk-reward balance meaningfully. Add in the yield advantage over Treasuries and the absence of meaningful credit risk, and the case for including agency mortgage backed securities grows stronger.
The sector will still experience periods of underperformance relative to other fixed-income choices. Spreads can widen. Prepayment models can prove imperfect. Housing market activity can surprise. Yet the structural features that once created outsized pain have largely run their course. Investors who understand those features and size their exposure accordingly stand in a better position today than they did several years ago.
For anyone managing a bond allocation, taking a fresh look at the sector makes sense. The combination of higher yields, more stable duration, and deep market liquidity is not permanent, but it is available now. That opportunity is worth examining carefully before conditions shift again.
The income stream continues month after month. The government-related backstop remains in place. And the prepayment option that investors sold to homeowners currently carries far less value than it did when rates sat much closer to outstanding coupons. Those three elements together create a setup that feels more constructive than it has in quite some time.
Whether rates ultimately peak near current levels or push modestly higher, the worst of the extension risk appears behind us. That alone changes the conversation around these securities and opens the door for a more permanent role in diversified fixed-income portfolios.
