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Black & Scholes : Theta θ
Issued on July 18 2011 par Strategies-options.com
Theta θ represents Time decay in the Black & Scholes model, and is the first derivative of an option price with respect to the time.
Theta θ is just a way to represent how time impacts option value every day.
I - Time needs to be inverted
Because we derive the theta as time goes by to expiry, then
Θ = ∂ V / ∂ t
Θ = ( ∂ V / ∂ τ ) . (∂ τ / ∂ t )
τ = T-t
∂ τ / ∂ t = -1
Θ = - ( ∂ V / ∂ τ )
II - Maths and Graphs
The Call case
Θ = - ( ∂ C / ∂ τ )
Θ = - ( ∂ [exp ( - q.τ ) . S . N( d1 ) - exp ( - r.τ ) . K . N( d2 ) ] / ∂ τ )
Θ = - ( S . σ / 2√τ ) . N’( d1 ) - r exp ( - r.τ ) . K . N( d2 )

The Put case
Θ = - ( ∂ P / ∂ τ )
Θ = - ( ∂ [ - exp ( - q.τ ) . S . N( - d1 ) + exp ( - r.τ ) . K . N( - d2 ) ] / ∂ τ )
Θ = - ( S . σ / 2√τ ) . N’( d1 ) + r exp ( - r.τ ) . K . N( - d2 )

Next : Black & Scholes : Vega υ
Previous: Black & Scholes : Gamma Г
Pdf connexes :
- Understanding N(d1) and N(d2) : Risk-Adjusted Probabilities in the Black-Scholes Model
- Black-Scholes Option Pricing Model
OPTIONS PRICING MODEL - INDEX
OPTIONS PRICING MODEL - INDEX
OPTIONS PRICING MODEL - CHAPTER I
OPTIONS PRICING MODEL - CHAPTER II
OPTIONS PRICING MODEL - CHAPTER III
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