Theta: how time decay quietly eats option value

Buy an option and, in a quiet market where nothing moves, it still loses value by tomorrow. That slow bleed is theta — time decay — and it's one of the defining features of options.

Why it happens

An option is partly a bet on future movement. Every day that passes, there's less future left for that movement to happen in, so the option is worth a little less. At expiration, an option is worth only its intrinsic value — whatever it's actually in-the-money by, and nothing for time.

The acceleration

Theta isn't constant. Time decay speeds up as expiration approaches, which is why the final days of an option's life can be brutal for buyers. It's also the entire reason zero-days-to-expiration options behave so violently: they're living through the steepest part of the decay curve in a single session.

What it means for how you trade

• If you're buying options, you're paying rent on time. You need the move to happen fast enough to outrun the decay. "It'll get there eventually" is how buyers lose money even when they're right.
• If you're selling options, theta works for you — but in exchange you take on risk that can dwarf the premium collected, which is its own discipline problem.

You don't need to calculate theta to respect it. You do need to know it's there, ticking against you every day you hold a long option — and to size and time accordingly.

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This article is educational and does not constitute investment advice or a recommendation. Options trading involves substantial risk and is not suitable for every investor. Autopilot Options does not guarantee profits or prevent losses. Past performance and historical data do not guarantee future results.