The Q  (Theta)              


Q How much does the option price change if the expiration date of the option is changing by a small amount (e.g. 1 day)?


You own a CALL option for some stock. The expiration date for the option is 300 days from now. The option has a value of $4. If the expiration date would be 1 day earlier the value of the option for a lifetime of 299 days would be $3.98. The Q for the stock option is

the difference in option price: $3.98 - $4.00 = - $0.02

divided by

the change of current date: 1 day = 1/365 years


Q = -$0.02 / 1/365 years = -7.3


As with r this value for T assumes that you state option prices in Dollars and measure the lifetime of your option in years. The  Q  tells you the effect of the passing of time towards expiry on the option price. To understand how  Q  depends on all other quantities go back to the OPTIONATOR!


And the last of the basic greeks ...