Shifting Yield Curves
Shifting Yield Curves
The yield curve is a snapshot of yields across maturities at a single moment in time. But curves shift shape constantly—parallel shifts, steepening, flattening, twists. Understanding how your portfolio responds to different curve moves is essential to managing duration risk beyond simple averages.
Key takeaways
- Parallel shifts (all yields move by the same amount) are the simplest curve movement.
- Non-parallel shifts (steepening or flattening) affect bonds of different maturities unequally.
- Portfolio average duration can mask exposure to curve risk.
- Curve twist (short rates move differently than long rates) creates basis risk.
- Scenario analysis across curve shapes reveals true portfolio risk.
The Yield Curve and Its Movements
The yield curve plots the yield of Treasury securities (or other risk-free bonds) against maturity. On a typical day in 2023, the curve might look like:
- 2-year: 5.0%
- 5-year: 4.5%
- 10-year: 4.2%
- 30-year: 4.0%
This is a downward-sloping or "inverted" curve—unusual, and typically a sign of economic stress. More typical curves in 2010–2019 were upward-sloping:
- 2-year: 1.8%
- 5-year: 2.1%
- 10-year: 2.3%
- 30-year: 2.7%
The curve changes shape constantly in response to Fed policy, inflation expectations, economic growth forecasts, and risk demand. Understanding these movements is critical for bond portfolio management.
Parallel Shifts
A parallel shift occurs when all yields across all maturities move by the same amount. In practice, parallel shifts are rare and approximate—there's always some difference between how short and long rates move. But they happen often enough to warrant special attention.
Suppose every yield on the Treasury curve rises by 1%:
- 2-year: 5.0% → 6.0%
- 5-year: 4.5% → 5.5%
- 10-year: 4.2% → 5.2%
- 30-year: 4.0% → 5.0%
In a parallel shift up, all bonds lose value based on their duration. A portfolio with average duration 5 years loses approximately 5%. A portfolio with average duration 8 years loses approximately 8%. The shape of the portfolio—which specific maturities it owns—doesn't matter, only the average duration.
This is why duration is such a powerful tool: in parallel shift environments, it captures almost all the risk. A bond fund manager can state, "This portfolio has 6-year duration," and investors immediately know the expected loss if yields rise 1% uniformly across the curve.
However, parallel shifts explain only 80–90% of yield curve movements. The other 10–20% comes from shape changes.
Non-Parallel Shifts: Steepening
A steepening occurs when long yields fall relative to short yields (or rise more slowly). The curve becomes steeper.
From the starting point:
- 2-year: 5.0%, 5-year: 4.5%, 10-year: 4.2%, 30-year: 4.0%
A steepening might look like:
- 2-year: 5.0%, 5-year: 4.4%, 10-year: 4.0%, 30-year: 3.8%
The 2–30 curve spread (difference in yields) widened from 1% to 2%. Long bonds outperformed because their yields fell.
Why does this matter? Because a portfolio with short-duration bonds (concentrated in 2–3 year maturities) would perform differently from a portfolio with long-duration bonds (concentrated in 10–30 year maturities) in a steepening.
Short-duration portfolio (average duration 3 years):
Yields up by 0% → price gain from falling yields ≈ 0%.
Long-duration portfolio (average duration 15 years):
Yields down by 0.2% → price gain from falling yields ≈ 15 × 0.2% = +3%.
Both portfolios have the same average duration statement—"long-term interest rate sensitivity"—but their actual returns diverge when the curve steepens.
Steepening often occurs during economic recoveries or Fed tightening cycles, because investors expect near-term rate increases (pushing short rates up) but longer-term growth to eventually stabilize (keeping long rates relatively lower). This was evident in 2022–2023, when the Fed raised short rates aggressively while long rates rose more modestly.
Non-Parallel Shifts: Flattening
A flattening is the opposite: long yields rise relative to short yields (or fall less). The curve becomes flatter.
From the starting point, a flattening might look like:
- 2-year: 4.8%, 5-year: 4.6%, 10-year: 4.5%, 30-year: 4.4%
The 2–30 curve spread narrowed from 1% to 0.4%. Short bonds outperformed because their yields fell relative to long bonds.
A short-duration portfolio benefits in a flattening. A long-duration portfolio suffers. Yet both have the same duration exposure to parallel yield moves.
Flattening often occurs before recessions, as investors flee to long-term safety and the Fed considers rate cuts. During the 2018–2019 period, the curve flattened and then inverted, a classic pre-recession signal. Portfolios holding long-duration bonds (TLT, long corporates, long TIPS) outperformed broad bond indices in 2019 and early 2020, because the flattening and eventual yield collapse boosted long-bond returns beyond what duration alone would suggest.
Curve Twists and Basis Risk
A twist is when the entire curve inflects—the slope change is not uniform. Short rates might rise, long rates fall, and medium rates stay roughly flat. Or rates at 5–7 year maturities might behave differently from both short and long rates.
Twists create basis risk: bonds with similar duration but different maturities perform differently. A 5-year bond with duration 4.8 years and a 10-year bond with duration 9 years might both have similar convexity but different exposure to a twist.
For example, in 2022, short-term rates rose faster than long-term rates (classic steepening). But in mid-2023, the curve went through a twist where middle maturities (5–7 years) underperformed both very short (2-year) and very long (20–30 year) maturities. A barbell portfolio (owning mostly 2-year and 30-year bonds, skipping middle maturities) would have outperformed a bullet portfolio (owning mostly 10-year bonds) despite having similar average duration.
Professional bond managers exploit twists and curve shape changes by tilting their portfolios. But most passive investors don't have this flexibility. Understanding that your broad bond fund (BND, AGG, VBTLX) is implicitly taking on curve shape risk—owning bonds across all maturities—is important for long-term expectations.
Portfolio Duration as an Average, Not a Complete Picture
A bond fund reports "effective duration 5.5 years." What does this mean for risk? In a parallel shift, a 1% yield move causes a 5.5% price change. But if the portfolio is weighted heavily toward 2–3 year bonds (ladder strategy) or heavily toward 20–30 year bonds (bullet strategy), the actual behavior in a twist or steepening could differ significantly.
A portfolio with duration 5.5 years distributed as:
- 50% in 2-year bonds (duration 1.9), 50% in 10-year bonds (duration 8.2)
Has average duration = 0.5 × 1.9 + 0.5 × 8.2 = 5.05 years.
But in a steepening where 2-year yields rise 1% and 10-year yields fall 0.5%, the portfolio loses 0.5 × 1.9 × 1% = 0.95% and gains 0.5 × 8.2 × 0.5% = +2.05%, for a net gain of 1.1%.
A portfolio with the same 5.05-year duration but distributed across all maturities uniformly would behave differently in that steepening scenario. This is why scenario analysis—calculating returns under different curve shapes—is essential for professional management.
Historical Curve Movements
From 2007 to 2008, the curve steepened dramatically as the Fed cut short rates to near zero while long rates fell more modestly. Investors holding long-dated bonds made substantial capital gains.
From 2008 to 2011, the Fed held short rates at zero while gradually reducing long-term rates through asset purchases (quantitative easing). Long bonds handily outperformed short-duration securities.
From 2017 to 2019, the curve flattened aggressively as the Fed raised short rates while long-term growth expectations moderated, keeping long yields stable. Long bonds outperformed despite (and partly because of) their duration exposure.
From 2020 to 2022, the curve steepened dramatically as the Fed kept short rates near zero while long rates rose from 0.7% to nearly 4%. The steepening initially helped long bonds' relative performance, but the absolute yield rise hurt all bonds. By year-end 2022, TLT was down 29%, but shorter-duration bonds (IEF, 7–10 year Treasuries) were down only 10%, because steepening could not fully offset the yield rise's effect.
Analyzing Your Portfolio
Next
Yield curve shifts are one source of price movement, but they're not the only one. Different maturities respond differently to certain types of rate moves, a phenomenon captured by key rate duration. Understanding how rates at specific maturities—2-year, 5-year, 10-year—affect your portfolio reveals hidden risks.