💵 Fixed Income

Bond Duration & Convexity — Modified, Macaulay & Effective Duration

Bond duration and convexity formulas explained. Modified duration, Macaulay duration, effective duration, and convexity with calculation examples.

Key Concepts

Duration

Measure of bond price sensitivity to yield changes. Higher duration = more price volatility. Approximate % price change for 1% yield change.

Macaulay Duration

Weighted average time to receive cash flows. In years. Duration of zero-coupon = maturity.

Modified Duration

ModDur = MacDur / (1 + y/m). ΔP/P ≈ -ModDur × Δy. Direct measure of price sensitivity.

Convexity

Curvature of price-yield relationship. Duration is linear approximation; convexity corrects for non-linearity. Positive convexity: good for investor.

Duration Properties

Higher for: longer maturity, lower coupon, lower yield. Portfolio duration = weighted average of bond durations.

Formulas

From this module

Modified Duration

ModDur = MacDur / (1 + y/m)

Where: y = YTM, m = compounding periods per year

Price Change (Duration)

ΔP/P ≈ -ModDur × Δy

Where: First-order approximation

Price Change (Duration + Convexity)

ΔP/P ≈ -ModDur × Δy + ½ × Convexity × (Δy)²

Where: More accurate with convexity adjustment

Effective Duration

EffDur = (P- - P+) / (2 × P0 × Δy)

Where: Used for bonds with embedded options

Effective Convexity

EffConv = (P- + P+ - 2P0) / (P0 × Δy²)

Where: Curvature correction

Master Formula Sheet -- Fixed Income

Bond Price

P = Σ[C/(1+r)ᵗ] + FV/(1+r)ⁿ

PV of coupons + PV of par

Current Yield

CY = Annual Coupon / Price

Income return only

YTM

Rate that equates PV of all CFs to price

Total return if held to maturity

Macaulay Duration

MacD = Σ[t × PV(CFₜ)] / Price

Weighted average time to receive CFs

Modified Duration

ModD = MacD / (1 + YTM/m)

Price sensitivity to yield change

Price Change (Duration)

ΔP/P ≈ -ModD × Δy

First-order approximation

Price Change (with Convexity)

ΔP/P ≈ -ModD × Δy + ½ × Convexity × (Δy)²

More accurate for large yield changes

Effective Duration

EffD = (P₋ - P₊) / (2 × P₀ × Δy)

For bonds with embedded options

Credit Spread

Spread = YTM_corporate - YTM_benchmark

Compensation for credit risk

Expected Loss

EL = PD × LGD × EAD

PD=prob default, LGD=loss given default

Decision Frameworks

How to manage interest rate risk?

Use when:

  • Match duration of assets and liabilities (immunization)
  • Extend duration if expecting rates to fall
  • Shorten duration if expecting rates to rise

Avoid when:

  • Using Macaulay duration for callable bonds (use effective duration)
  • Ignoring convexity for large yield changes

Test Your Understanding

If a bond has a modified duration of 6 and yields increase by 100 basis points, the approximate price change is:

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