Theta

The daily rate at which an option loses value as time passes — called time decay. Theta works in favor of option sellers and against option buyers.

Theta measures how much an option's price decreases with each passing day, holding all else constant. An option with a theta of -0.05 loses $5 in value per day (0.05 × 100 shares per contract). This decay is not linear — it accelerates dramatically in the final weeks before expiration as the probability of a meaningful price move decreases with less time remaining.

Theta is the reason that buying options is a time-sensitive bet. A call buyer who is directionally correct but wrong about timing can still lose money: the stock can move in the anticipated direction while the option loses value faster through time decay than it gains from the price movement. For far out-of-the-money options with short expirations, a stock move of 5% in the correct direction might produce a 50% loss in the option because the move wasn't large enough to overcome theta.

Selling options puts theta on your side. A covered call seller and a cash-secured put seller are essentially selling time — they collect premium today and root for the option to expire worthless, at which point theta has done its work and the entire premium collected becomes profit. The "theta decay trade" is the core mechanic behind all premium-collection strategies, from simple covered calls to complex iron condors.

This definition is for informational and educational purposes only. Nothing on Finance Compass constitutes financial, investment, or trading advice. Always conduct your own research and consult a qualified professional before making financial decisions.