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Binary Option : theta
Issued on July 10 2011 par Strategies-options.com

Time decay for binary options is less important than for vanillas ones.
I - Intuition

Before Expiry:
The more the binary option is out of the money, the less the chance it would be in.
Conversely, the more the binary option is in the money, the more the chance it would be in.

That leads to :
OTM Binary -> theta θ <0
ITM Binary -> theta θ >0


Hence, there is some area where theta θ is zero
If interest rates are set to zero,
Binary theta is zero for a spot S at

S(θ=0)=(exp(-0.5*σ²*T))*K

where σ is annualized volatility, T is annual time to maturity and K the strike.

For example :
If interest rates are zero, for a 6 months binary call or put struck at 100, theta is zero for spot at 100*exp(-0.5*0.30*0.30*0.5)=97.775


Binary Option Expiry:
Decay is magnified at expiry because ITM binary tends to be worth $1 and OTM binary tends to be worthless.



II- Black & Scholes Binary Option Theta

Binary Call Theta :
Θ = exp ( - r.τ ) . N( d2 ) + exp ( - r.τ ) . N’( d2 ) . [( d1 / (2 τ) ) – ( (r-q) / (σ / √τ) ) ]

Binary Put Theta :
Θ = [ exp ( - r.τ ) . ( 1 - N( d2 ) ) ] - exp ( - r.τ ) . N’( d2 ) . [( d1 / (2 τ) ) – ( (r-q) / (σ / √τ) )]



III - 3D graph

For a binary 100 call


For a binary 100 put




Next : Binary Options : Vega
Previous : Binary Option : Gamma

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Other Derivatives - INDEX
Other Derivatives - CHAPTER I
Other Derivatives - CHAPTER II
Other Derivatives - CHAPTER III
Other Derivatives - CHAPTER IV

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