Theta and Time Decay Explained

Written by the MarketWrench team. Examples are worked with the same Black-Scholes model used in our calculators (4% rate, no dividends unless stated) and are reviewed for accuracy before publishing. How we create content.

Every option has an expiration date, and every day closer to it removes a little of the option's value. That steady loss is called time decay, and the Greek that measures it is theta. For option buyers it is a constant headwind. For sellers it is the main source of profit.

What theta means

Theta estimates how much an option's price drops from one day passing, if nothing else changes. A theta of −0.05 means the option is expected to lose about $0.05 per share, or $5 per contract, per day. Long options have negative theta. Short options have positive theta, because the seller gains as the price they owe falls.

Why options decay at all

Part of an option's price is extrinsic value, the value of the chance that the stock moves in the buyer's favor before expiration. With less time left there are fewer chances, so that value shrinks. At expiration it hits zero, and only intrinsic value remains.

Decay is not a straight line HYPOTHETICAL

Which options decay fastest

• At-the-money options have the most extrinsic value, so they lose the most dollars per day.
• Short-dated options decay faster than long-dated ones, especially in the last two to three weeks.
• High-IV options carry more extrinsic value, so they have more to lose.
• Deep ITM or far OTM options have little extrinsic value, so their theta is small in dollars.

What it means for buyers

If you buy a call or put, you need the stock to move far enough, soon enough, to outrun decay. Buyers often choose more time than they think they need (60–120 days) and close the trade before the final month, when decay is steepest.

What it means for sellers

Sellers of covered calls, cash-secured puts, credit spreads and iron condors collect decay. Many choose 30–45 days to expiration, where decay is meaningful but there is still time to adjust. The catch: positive theta comes with negative gamma, so a sharp move can wipe out weeks of decay in a day.

Strategies built around decay

The calendar spread sells a fast-decaying near-term option and buys a slower-decaying longer one. The poor man's covered call does the same with a deep ITM long-term call. Both try to profit from the gap between two decay rates.

Common mistakes

• Buying weekly options and expecting the stock to "eventually" move. Time runs out quickly.
• Assuming theta is constant. It changes daily and jumps near expiration.
• Selling options only for theta while ignoring how much a big move could cost.
• Forgetting weekends. Calendar time passes on weekends too, and prices often reflect that ahead of time.

See theta for any option in the Black-Scholes calculator, or read how to read the option Greeks.

FAQ

Does theta apply on weekends?
Time passes every calendar day. Markets tend to price weekend decay in ahead of time, so you may not see a jump on Monday.

Is positive theta free money?
No. Sellers earn decay in exchange for taking on the risk of large moves.

When is time decay fastest?
In the final few weeks before expiration, especially for at-the-money options.

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How to Read the Option Greeks · How to Pick a Strike and Expiration · All Learn articles