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Define “Theta” and Its Impact on Option Value over Time.

Theta is the "time decay" Greek, measuring the decrease in an option's price for every day that passes, all else being equal. It is always negative for long option positions.

Theta decay accelerates as the option approaches expiration, meaning the option loses value at an increasing rate, particularly impacting Out-Of-The-Money and At-The-Money options.

How Does Theta Affect the Value of an Option as Expiration Approaches?
Which Greek Letter Measures the Rate of Time Decay?
How Does the Time to Expiration (Theta) Interact with IV to Affect the Bid-Ask Spread of an Option?
What Role Does Theta Play in the Decay of an Option’s Extrinsic Value?