Parallel shift
Also written Parallel yield curve shift · Parallel shift in the yield curve
A change in the term structure in which all rates move in the same direction by the same extent, leaving the spread between short and long rates unchanged — the only kind of move duration handles well.
In plain language
A yield curve is a snapshot. The workbook says what matters more than its shape is how it changes over time, and calls those changes term structure shifts.
There are three kinds, described by the relative moves of the long-term rate (LR) and short-term rate (SR): parallel, steepening and flattening.
A parallel shift is the simplest: all rates move in the same direction by the same extent. Lift the whole curve up by 10 basis points, or drop it by 10, and every point moves together. The spread between long and short rates does not change — and neither does the curve's shape.
Parallel shifts matter disproportionately because the most widely used risk measure, duration, quietly assumes them.
How it works
The workbook's table of shifts, from a starting curve of SR 7.00% and LR 8.00% (spread +1.00%, normal):
| After SR | After LR | Spread | Shift |
|---|---|---|---|
| 7.10% | 8.10% | +1.00% | Parallel |
| 6.90% | 7.90% | +1.00% | Parallel |
| 6.90% | 8.10% | +1.20% | Steepening — twist |
| 7.10% | 7.90% | +0.80% | Flattening — twist |
| 7.10% | 8.20% | +1.10% | Steepening — convexity change |
And from a flat curve at 8.00% / 8.00%, moves to 8.10% / 8.10% or 7.90% / 7.90% are parallel, and the curve stays flat.
The test is the spread: if the spread between LR and SR is unchanged, the shift is parallel.
Why it matters for risk. Modified duration approximates the percentage change in bond price for a change in yield — and the workbook states that it "is accurate only for very small and parallel shifts in the yield curve". A duration-based hedge assumes the portfolio and the hedging instrument see the same yield change. When the curve steepens or flattens instead, bonds at different maturities move by different amounts, and a book that was duration-neutral no longer is. For large moves, even a parallel one, convexity makes duration inaccurate.
A worked example
Illustrative bonds. The duration approximation is the workbook's: % price change ≈ − modified duration × change in yield.
A fund holds Rs 10 crore of a 2-year bond with modified duration 1.8 and Rs 10 crore of a 10-year bond with modified duration 7.0. The curve starts at SR 7.00%, LR 8.00%.
A parallel shift up of 10 basis points — SR 7.10%, LR 8.10%:
| Bond | Change in yield | Approximate price change | Rupee change |
|---|---|---|---|
| 2-year | +0.10% | −1.8 × 0.10% = −0.18% | −Rs 1,80,000 |
| 10-year | +0.10% | −7.0 × 0.10% = −0.70% | −Rs 7,00,000 |
| Total | −Rs 8,80,000 |
A single portfolio duration — the value-weighted (1.8 + 7.0) ÷ 2 = 4.4 on Rs 20 crore — gives the same answer: 4.4 × 0.10% × Rs 20 crore = Rs 8,80,000. One number describes the whole book, because every yield moved by the same amount.
Now a steepening twist — SR 6.90%, LR 8.10%:
| Bond | Change in yield | Rupee change |
|---|---|---|
| 2-year | −0.10% | +Rs 1,80,000 |
| 10-year | +0.10% | −Rs 7,00,000 |
| Total | −Rs 5,20,000 |
The portfolio duration of 4.4 has no single yield change to multiply. The book's loss depends on the shape of the move, which is exactly what a parallel-shift measure cannot see.
Why NISM asks about it
Chapter 1 (Introduction to Interest Rate, Interest Rate Instruments and Fixed Income Markets) defines parallel, steepening and flattening shifts in its term structure section with the SR/LR table, and returns to parallel shifts in section 1.12.8 on convexity, where modified duration is described as accurate only for very small and parallel shifts. Chapter 5 builds duration-based hedging on that assumption. Expect a question that gives before-and-after short and long rates and asks you to classify the shift.
Common exam traps
- Parallel means same direction and same extent — so the spread is unchanged.
- Both rates moving the same direction by different amounts is not parallel. The workbook calls that a convexity change, and it is a steepening or flattening.
- Rates moving in opposite directions is a twist, never parallel.
- A flat curve that shifts in parallel stays flat.
- Modified duration is accurate only for very small and parallel shifts. Large moves need convexity; non-parallel moves break single-number duration.
- Duration-neutral does not mean curve-neutral. A steepening or flattening can hurt a book hedged on duration alone.
Check yourself
1.The short rate moves from 7.00% to 6.90% while the long rate moves from 8.00% to 8.10%. How is this shift in the term structure classified?
- a)Steepening – twist
- b)Steepening – convexity change
- c)Flattening – twist
- d)Parallel shift
Show the answer
Answer: (a) Steepening – twist
Apply the two-step test. Step 1 — the spread. It was +1.00% (8.00 − 7.00) and is now +1.20% (8.10 − 6.90). The gap between the long and short rate has widened, so this is a steepening (the curve rotates anti-clockwise). Step 2 — how did they move? The short rate fell while the long rate rose — opposite directions, which the workbook labels a twist. Had both moved in the same direction by different amounts, or had one stayed constant, it would have been a convexity change instead. A parallel shift would require the spread to be unchanged.
Where this is taught
Free preparation for NISM Series IVRelated terms
- Modified DurationMacaulay's duration divided by (1 + yield) — the percentage by which a bond's price moves for a one percentage point change in interest rates, and so the standard measure of interest rate risk.
- ConvexityThe curvature of the price-yield relationship — the correction duration misses, because duration is a straight line and the true relationship bends.
- Duration-based hedge ratioThe number of interest rate futures that drives a bond portfolio's duration to zero — portfolio modified duration times market value, divided by futures modified duration times futures price over par.
- Inter-bond spreadA long-short position in futures on two different GOI bonds, usually of the same expiry, taken to express a view on how the yield curve will steepen or flatten.
- Term structure of interest ratesInterest rate plotted against term — one curve per credit quality, with the risk-free curve as the base and every other borrower quoted as a spread over it.
- TwistA steepening or flattening of the yield curve in which short-term and long-term rates move in opposite directions — as distinct from a convexity change, where they move the same way by different amounts or one stays put.
- Term spreadThe difference in yield between two bonds of the same issuer at different maturities — the workbook's own example is the gap between a 10-year and a 2-year G-Sec.
- Three S's of the yield curveThe workbook's own name for the three ways a yield curve can move — Shift, Slope and Shape — that a fixed income manager watches when taking an interest-rate view.