Treasury vs. Corporate vs. Agency Markets Overview

Beginner | Published: 2025-10-29

Three Markets, Three Risk Profiles

The U.S. fixed-income market exceeds $58 trillion in total debt outstanding, but that headline figure masks a structural divide every bond investor needs to understand. Treasuries, corporates, and agency securities each carry fundamentally different risks, and the yield differences between them are not just numbers — they reflect specific compensation for specific exposures.

Treasuries pay you for lending to a sovereign currency issuer. Corporates pay you for bearing default and liquidity risk. Agencies pay you for absorbing prepayment and convexity risk. Mixing these up — or treating all yield as equivalent — leads to portfolio construction mistakes that show up precisely when markets get difficult.

Treasury Securities: The Benchmark Everything Else Is Priced Against

What they are: Debt obligations of the U.S. government, backed by its full faith and credit — meaning the constitutional power to tax and, uniquely, to issue the currency in which the debt is denominated.

Market size: Approximately $29.7 trillion outstanding as of Q3 2025 (SIFMA), representing over 60% of all U.S. debt securities excluding securitized products. This is the deepest, most liquid bond market in the world, with average daily trading volume exceeding $900 billion.

The credit profile: Default probability on dollar-denominated U.S. Treasuries is treated as zero for pricing purposes. The government has never defaulted on its marketable debt in modern history. Whether this constitutes true “risklessness” is a philosophical question — but it is the practical reality that underpins all fixed-income pricing.

The tax advantage most investors overlook: Treasury interest is exempt from state and local income taxes. In high-tax states, this matters significantly. A Treasury yielding 4.5% in a state with a 10% income tax bracket has a state-tax-equivalent yield of 5.0% (calculated as 4.5% ÷ (1 − 0.10)). For a California or New York investor comparing a Treasury to a corporate bond, the after-tax gap is narrower than the nominal spread suggests. Always compare on an after-tax basis.

Duration and convexity: Non-callable Treasuries exhibit positive convexity — they gain more in price when rates fall than they lose when rates rise by an equivalent amount. This makes them the cleanest expression of interest rate risk, which is why they serve as the hedging instrument for virtually all fixed-income portfolios. A 10-year Treasury has roughly 8 years of modified duration; a 30-year, roughly 17 years.

Why this matters: Every other bond in the market is priced as “Treasury yield plus a spread.” When someone says a corporate bond trades at “150 over,” they mean 150 basis points above the comparable-maturity Treasury. Understanding Treasuries is not optional — it is the foundation.

Agency Securities: Government-Adjacent With a Hidden Option

What they are: Debt issued or guaranteed by government-sponsored enterprises (GSEs) — primarily Fannie Mae, Freddie Mac, and Ginnie Mae. Ginnie Mae securities carry an explicit full-faith-and-credit government guarantee. Fannie and Freddie carry an implicit guarantee, powerfully reinforced when the government placed both into conservatorship in September 2008 rather than allowing default.

Market size: Agency MBS alone total approximately $9.4 trillion outstanding. Ginnie Mae’s portfolio stands at roughly $2.8 trillion (mid-2025). Daily trading volume in agency MBS averages around $300 billion, making it the second most liquid fixed-income market after Treasuries.

The credit profile: Near-zero default risk. The 2008 financial crisis was the stress test: when the housing market collapsed, the government stepped in. The implicit guarantee proved real. Investors holding agency MBS through 2008-2009 suffered no credit losses.

Prepayment risk — the defining feature: This is what separates agencies from every other bond market segment. Agency MBS give homeowners the right to refinance their mortgages at any time. When rates fall, refinancing activity surges, and MBS investors get their principal returned early — right when they would most prefer to keep earning the higher coupon. When rates rise, prepayments slow to a crawl, and the bond’s effective maturity extends — right when investors would prefer to get their money back and reinvest at higher rates.

This two-sided problem has a name: negative convexity. Unlike Treasuries, which gain more than they lose from equal rate moves, agency MBS gain less when rates fall (because prepayments accelerate and cap the upside) and lose more when rates rise (because extension lengthens the bond’s effective duration). The spread agencies pay over Treasuries is primarily compensation for this convexity cost, not for credit risk.

Duration instability: A 30-year agency MBS pass-through might have an effective duration of 6 years in a stable rate environment. If rates drop 100 basis points, that duration could contract to 3 years as prepayments surge. If rates rise 100 basis points, duration could extend to 9 years. This moving target makes agency MBS harder to hedge and harder to fit into a duration-matched portfolio than Treasuries or even corporates.

Yield: Agencies typically trade 50-80 basis points above comparable Treasuries. That spread compensates almost entirely for prepayment and convexity risk rather than credit risk.

Corporate Bonds: Credit Risk for Extra Yield

What they are: Debt issued by corporations ranging from AAA-rated multinationals to CCC-rated distressed borrowers. The corporate market splits into two distinct worlds: investment-grade (rated BBB− and above) and high-yield (BB+ and below).

Market size: Approximately $11.4 trillion outstanding as of early 2025. Investment-grade issuance hit $1.82 trillion in 2025. High-yield issuance runs considerably smaller, typically $250-350 billion annually.

The tax reality: Unlike Treasuries, corporate bond interest is fully taxable at federal, state, and local levels. An investor in a 37% federal bracket plus 10% state tax faces an effective combined marginal rate near 43%. A corporate bond yielding 5.8% nets roughly 3.3% after tax, while a Treasury at 4.5% nets about 3.5% after combined taxes (since Treasuries are state-tax-exempt). The corporate bond with the higher nominal yield actually delivers less after-tax income in this scenario. Run the numbers for your own tax situation before assuming the corporate spread is free money.

Investment-grade credit risk (quantified):

Typical IG spreads of 100-150 basis points over Treasuries far exceed expected credit losses of 3-18 basis points. The gap represents liquidity premium (corporate bonds trade less frequently, with wider bid-ask spreads) and a risk-appetite premium (compensation for the tail risk of severe credit events and for holding an asset that becomes illiquid precisely when you most need liquidity).

High-yield credit risk:

High-yield spreads of 300-500 basis points look generous until you subtract expected losses. A B-rated bond paying 350 basis points over Treasuries with 230 basis points of expected annual loss offers roughly 120 basis points of true excess compensation — and that assumes an average default year, not a recessionary one.

Duration and convexity: Investment-grade corporates typically exhibit positive convexity similar to Treasuries, though slightly less because many corporate issues contain call provisions. Callable corporates behave more like agency bonds in falling-rate environments — the issuer can redeem the bond early, capping investor upside. Non-callable corporates with similar maturities will have modestly lower duration than equivalent Treasuries because their higher coupons return cash faster.

Comparing Across Segments

Note on yields: Specific yield levels change constantly with market conditions. Rather than anchoring to point-in-time numbers that will become stale, focus on the spread relationships above. You can find current yields on FRED (Federal Reserve Economic Data) by searching for Treasury constant-maturity rates, the ICE BofA Corporate Index OAS, and the Bloomberg U.S. MBS Index yield.

Where Investors Go Wrong

Comparing nominal yields without adjusting for taxes. A 5.8% corporate yield and a 4.5% Treasury yield are not 130 basis points apart for investors in high-tax states. After adjusting for state tax exemption on Treasuries, the real gap could be 50-80 basis points — far less compelling given the added credit and liquidity risk.

Ignoring the prepayment option embedded in agency MBS. Investors buy agency MBS for the “safe” yield pickup over Treasuries without understanding that negative convexity means the bond underperforms Treasuries in both sharply falling and sharply rising rate environments. The spread compensates for a real cost. The 2020-2022 rate cycle demonstrated this vividly: MBS investors who bought coupons near par in 2020-2021 watched their bonds extend dramatically as rates surged in 2022, amplifying losses beyond what a comparable-duration Treasury portfolio would have experienced.

Treating spread as pure profit. When IG spreads compress to the tightest decile of their historical range, investors are accepting the least compensation for credit and liquidity risk. In those environments, the after-tax, after-expected-loss advantage of corporates over Treasuries can shrink to near zero. Monitoring where spreads sit relative to their historical distribution matters more than the absolute level.

Overlooking liquidity asymmetry. Corporate bonds trade in a decentralized dealer market with meaningful bid-ask spreads that widen dramatically during stress. In March 2020, investment-grade bid-ask spreads ballooned past 100 basis points. Selling a $100,000 position cost over $1,000 in friction alone. Treasury markets, by contrast, saw increased volume and tightened spreads as capital fled to safety. The liquidity premium embedded in corporate spreads exists for a reason — it pays you for holding a bond you may not be able to sell cheaply when you most need to.

Putting This to Work

Start with your actual constraints: tax bracket, time horizon, and whether you can genuinely hold through a credit cycle without needing liquidity.

For the safety allocation in a portfolio, Treasuries remain the cleanest instrument — no credit risk, no prepayment risk, positive convexity, and favorable tax treatment in many states. Agency MBS offer a yield increment, but only if you understand and accept the convexity trade-off; they are not simply “Treasuries with more yield.”

Investment-grade corporates make sense as a deliberate credit allocation when spreads adequately compensate for the combined risks of default, illiquidity, and tax drag. Evaluate that compensation on an after-tax, after-expected-loss basis rather than on headline spread alone.

High-yield is a different asset class with equity-like drawdown characteristics during recessions. Treat it as a tactical position sized to your ability to absorb 10-15% peak-to-trough declines, not as a core income holding.

The comparative framework matters more than any single number: understand what risk each basis point of spread is paying you for, and you will build a fixed-income allocation that performs the way you expect — including in the environments when it matters most.