Spread Duration: Sensitivity to Credit Spreads

Key Takeaways

• Spread duration estimates the percentage price change of a bond for a 1% (100 basis point) change in its credit spread, holding the underlying risk-free rate constant.
• It answers a different question from ordinary duration: sensitivity to credit risk repricing rather than to a shift in the government yield curve.
• For a plain fixed-rate corporate bond the spread duration is close to its modified duration; for a floating-rate note it can be sizable even though rate duration is near zero.
• Scaled into dollars it becomes spread DV01, the profit or loss per one basis point of spread movement, which is how credit desks size and hedge positions.

What It Is

Spread duration is the sensitivity of a bond's price to a change in its credit spread. Formally, it is the approximate percentage change in price for a 100 basis point change in the spread:

Spread duration = -(1 / P) x (dP / ds)

where P is the price and s is the credit spread. A spread duration of 6 means that if the spread widens by 100 basis points, the price falls by roughly 6%, and if the spread tightens by 100 basis points, the price rises by roughly 6%.

The total yield on a corporate bond is the risk-free rate plus the credit spread. Modified duration captures sensitivity to the entire yield; spread duration carves out just the spread component, the part that moves with the market's view of default and downgrade risk.

The Intuition

A corporate bond's yield can rise for two very different reasons. Government yields might climb because the central bank is tightening, or the issuer's spread might widen because investors demand more compensation for its credit risk. Both push the price down, but they are separate risks that a manager may want to hedge separately.

Spread duration lets you split the exposure. Someone comfortable with the level of interest rates but nervous about a sector's creditworthiness cares about spread duration specifically. That is why credit indices and portfolio reports quote spread duration alongside rate duration rather than lumping them together.

How It Works

The working approximation mirrors the standard duration relationship, but the input is the spread move rather than the yield move:

Price change (%) is approximately -Spread duration x change in spread

To turn a percentage into money, desks use spread DV01 (sometimes written spread DVBP or CS01): the dollar change in a position's value for a one basis point move in spread.

Spread DV01 = Spread duration x Market value x 0.0001

A position with more spread duration or more market value carries a larger spread DV01. Two special cases matter:

• Fixed-rate corporate bond: because the spread is embedded in the same discounting as the rest of the yield, spread duration is roughly equal to modified duration.
• Floating-rate note: the coupon resets with short-term rates, so rate duration is tiny, yet the fixed spread over the reference rate is still discounted over the bond's life, leaving a meaningful spread duration.

Worked Example

Consider a $1,000,000 position in an investment grade corporate bond trading at par (price of 100) with a spread duration of 6.0.

First, the spread DV01:

Spread DV01 = 6.0 x $1,000,000 x 0.0001 = $600 per basis point

Now suppose the issuer's sector sells off and the bond's credit spread widens by 50 basis points, while government yields are unchanged. The estimated loss is:

Loss is approximately 50 x $600 = $30,000

As a percentage that is -6.0 x 0.50% = -3.0%, so the price falls from 100 to about 97 and the position drops to roughly $970,000. Had the spread tightened by 50 basis points instead, the position would have gained about $30,000. This figure captures only the spread move; if government yields had also risen, modified duration would add a separate loss on top.

Common Mistakes

1. Confusing spread duration with rate duration. They measure sensitivity to two different variables. A floating-rate note can have near-zero rate duration and still carry real spread duration.
2. Forgetting the sign. Spreads widening is bad for a long position: price falls. The negative sign in the formula is doing real work, not decoration.
3. Treating it as exact for large moves. Like ordinary duration, spread duration is a first-order estimate. For spread changes of several hundred basis points, convexity effects make the linear estimate too pessimistic on tightening and too optimistic on widening.
4. Ignoring it for Treasuries. A default-free government bond has essentially no credit spread, so its spread duration is effectively zero even though its rate duration can be large.
5. Mixing units. Spread DV01 uses one basis point (0.0001); the percentage formula uses the spread change in percent. Blending them scales the answer by 100.

Frequently Asked Questions

Q: What does spread duration measure? Spread duration measures the approximate percentage change in a bond's price for a 100 basis point change in its credit spread, with the underlying risk-free rate held constant. It isolates credit risk sensitivity from interest rate sensitivity.

Q: How is spread duration different from modified duration? Modified duration measures sensitivity to the entire yield, including moves in the government curve. Spread duration measures sensitivity only to the credit spread component. For a plain fixed-rate corporate bond the two numbers are close; for a floating-rate note they diverge sharply.

Q: What is spread DV01? Spread DV01, also called CS01, is spread duration expressed in dollars: the gain or loss on a position for a one basis point move in spread. It equals spread duration multiplied by market value multiplied by 0.0001, and credit desks use it to size and hedge exposures.

Q: Does a Treasury bond have spread duration? Essentially no. A default-free government bond carries no meaningful credit spread, so there is nothing for the spread to move. Its price sensitivity is captured by rate duration instead.

Q: Why does a floating-rate note still have spread duration? Its coupon resets with short-term rates, so rate duration is small, but the fixed spread paid over the reference rate is still discounted across the bond's remaining life. That embedded spread is what spread duration prices.

Sources

1. Investopedia. "Spread Duration." https://www.investopedia.com/terms/s/spreadduration.asp
2. Investopedia. "Duration." https://www.investopedia.com/terms/d/duration.asp
3. Investopedia. "Dollar Duration (DV01)." https://www.investopedia.com/terms/d/dollar-duration.asp
4. U.S. Securities and Exchange Commission. "Investor Bulletin: Interest Rate Risk and Bonds." https://www.sec.gov/investor/alerts/ib_interestraterisk.pdf

Disclaimer

This article is educational content only and is not financial advice. Nothing here is a recommendation to buy, sell, or hold any security. Consult a licensed advisor before making investment decisions.