Theta Decay Explained: How Time Decay Works in Options
Theta decay is the gradual loss of an option’s time value as expiration gets closer. Theta is the estimate of how much value a contract loses in one day if nothing else changes: the stock stays put and volatility holds steady. Option buyers pay that cost while they wait. Option sellers collect it, and take on risk in return.
Theta decay
An option’s price has two parts. One is intrinsic value, which is whatever the contract would be worth if exercised right now. The other is time value, the extra amount people pay for the chance that the stock moves in the contract’s favor before expiration. Theta decay is the steady erosion of that second part. On the expiration date, time value is gone and only intrinsic value remains.
Theta appears on any broker’s options chain, next to delta, gamma and vega. It is shown per share, so a theta of -0.05 means the contract is estimated to lose about 5 cents per share per day, which is about $5 per contract because one contract covers 100 shares. Treat it as an estimate from a pricing model, not a promise. The real price also reacts to the stock moving and to changes in implied volatility.
This is what makes options different from stock. Holding shares costs nothing extra for each day you hold them. Holding a long option carries a daily cost, even on days when the stock does nothing, and that cost is easy to miss because it shows up as a slowly shrinking price rather than a bill.
Time decay in options
Time decay is the same idea described from the price side. A contract with a lot of time left has a lot of time value to lose, but it loses that value slowly. A contract with only a few days left has little time value remaining, yet each day takes a larger share of what is left.
That is why the position can be worth less and still be decaying faster in percentage terms. A premium that looks small near expiration is often small because time has already taken most of it, and what remains can disappear quickly.
Which contracts carry the most decay risk depends on where the strike sits. At-the-money options hold the most time value, so they have the largest theta and the sharpest acceleration. Deep in-the-money options behave more like the stock itself and contain little time value to lose. Deep out-of-the-money options are cheap to begin with, so there is less premium left to decay in dollar terms, though they can still lose a large share of their price. The contracts in the middle, priced reasonably and looking reasonably likely to work, are where the decay bill matters most.
How fast does theta decay
Decay is not linear. It does not take an equal slice off the price every day. For at-the-money options, the daily loss tends to be modest when expiration is far away and then grows as the final weeks and days approach. The curve looks less like a straight line down and more like a slope that steepens toward the end.
Here is an illustrative example with round numbers. It is hypothetical, not a real trade or a recommendation. Suppose an at-the-money call has a theta of -0.04 with 45 days left. With 20 days left, the same kind of contract might show -0.07. With 7 days left, perhaps -0.12, and with 2 days left, perhaps -0.25. The stock has not moved in this example, and the daily cost has still grown several times over. Use your own chain for real values.
The practical reading is simple. If you buy a short-dated option, the stock has to make its move quickly or decay takes the premium by default. If you buy a longer-dated option, you pay more up front, but each day costs less and the move has more time to arrive.
Theta decay graph and chart
A theta decay chart usually plots an option’s time value on the vertical axis and days to expiration on the horizontal axis. For an at-the-money option the line starts high, falls gently for a long stretch, then curves downward more sharply and reaches zero at expiration. Some charts plot theta itself instead, and that line rises in size as the days run out.
When theta decay kicks in
Decay is there from the day the contract is listed. It does not switch on at some point. What changes is how visible it is. With several weeks left, the daily loss is small compared with normal price swings, so it is easy to ignore. In the last couple of weeks it becomes large enough to dominate, and for at-the-money options the last few days are usually the steepest part of the curve.
Does theta decay overnight and on weekends
Theta is quoted per day, and the price a contract trades at reflects the time left, so some decay shows up between one session and the next. How weekends and holidays are handled is not the same across pricing models and platforms. Some models count every calendar day, others weight trading days differently, and the theta your broker shows may follow either approach. Check your broker’s documentation to see how it treats days when the market is closed, and do not assume a fixed rule. Prices on the next open also reflect news and changes in volatility, which can outweigh decay entirely.
Sellers, buyers and the risk on each side
Because buyers lose time value, sellers gain it. A seller of an option collects premium up front and benefits as time value fades, provided the stock does not move against the position. That is the appeal of strategies such as covered calls and credit spreads.
The trade-off is risk, not free income. A seller takes on the obligation attached to the contract, and a large move in the stock can cost far more than the premium collected. Some short positions have capped risk and others do not, so read the contract specifications and your broker’s rules before selling anything. Buyers have the opposite profile: limited loss to the premium paid, but a daily cost that works against them until the stock makes a big enough move.
Trading involves risk of loss. Knowing theta tells you the size of the daily cost, not the outcome.
Quick answers
What is theta burn
Theta burn is informal shorthand for the value a long option loses to time passing. It is the same thing as theta decay, usually used when the loss feels fast, such as in the final days before expiration.
Is theta decay the same every day
No. For at-the-money options the daily loss generally grows as expiration nears, and the effect is smaller for deep in-the-money and far out-of-the-money contracts.
What is delta theta and gamma in options
Delta estimates how much the option price changes for a one-dollar move in the stock. Gamma estimates how fast delta itself changes. Theta estimates the daily loss from time passing.
Summary
Theta decay is the erosion of an option’s time value as expiration approaches, and theta is the estimated daily size of that loss with everything else unchanged. The pace is not even: at-the-money contracts tend to decay faster near the end, while deep in-the-money and far out-of-the-money contracts behave differently. Buyers fight decay, sellers collect it while accepting risk, and your broker’s rules decide how weekends and holidays are treated.
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