Derivatives option Greeks theta time decay option writing weekend decay

Theta decay

From WebNotes, a public knowledge base. Last updated 21 June 2026. Reading time ~12 min.

Key facts

What it measures	The change in an option's premium per one calendar day of time passing, with the underlying and volatility held constant
Sign for a buyer	Negative; a long option loses premium each day, so the holder is short theta
Sign for a seller	Positive in effect; a writer earns the decay each day, so the seller is long theta
Where it bites hardest	Theta accelerates as expiry nears; the last week of a contract decays far faster per day than a month out
What decays	Only the time value of the premium; intrinsic value does not decay, so deep in-the-money options have little theta relative to their price
Weekend decay	Theta accrues on every calendar day including weekends and holidays, so premiums can open lower on Monday from three days of decay

Theta is the option Greek that measures how much premium an option loses for each calendar day that passes, holding the underlying price and implied volatility constant. It is the daily cost of time. Theta is negative for an option buyer, who watches the premium erode every day, and works in favour of an option writer, who collects that decay; the time value of an option falls to zero at expiry, and theta tracks the pace of that fall. The decay is not steady: it accelerates sharply in the final days of a contract.

A long Nifty call with a theta of -8 loses about eight rupees of premium per day, per unit, from time alone, even if the Nifty 50 does not move and volatility holds. Over a five-day week that is forty rupees of decay the underlying must overcome before the buyer breaks even. This article defines theta precisely, separates the time value that decays from the intrinsic value that does not, explains why writers are long theta and buyers short theta, sets out the acceleration near expiry, and covers the weekend decay that catches holders out on a Monday open. For the premium that theta erodes, see option premium ; for the volatility Greek that often moves against the same positions, see vega .

Conflict-of-interest disclosure. This article is published by the WebNotes Editorial Team for informational purposes and is written independently. WebNotes operates a Zerodha account-opening referral programme, disclosed on the pages that carry the referral link; this article does not carry it and earns no referral commission from the concepts described here.

Definition and units

Theta is the partial derivative of the option premium with respect to time, expressed as the premium lost per calendar day. The Kite Greeks tab reports it per unit of the underlying, so a value of -8 on a Nifty call means the call sheds about eight index points of premium per day from the passage of time, with the underlying and volatility unchanged. Multiply by the lot size to get the rupee figure for a full position; on a 75-unit lot that -8 becomes about 600 rupees of decay a day for one long lot.

The sign convention reflects who holds the option. For the holder of a long option, theta is negative: time works against the position. Kite typically displays theta as a negative number for the long side. For the writer of a short option, the same decay is income, so the writer is described as long theta, and Sensibull’s strategy dashboard shows net theta as a positive number for a net-short-premium book, the daily carry the position earns if nothing else changes. Confirm which side the interface is showing before reading the sign; see how to read option Greeks on Kite .

Time value is what decays, not intrinsic value

Theta acts only on the time value, also called the extrinsic value, of the premium. An option’s premium splits into two parts: intrinsic value, the amount by which the option is in-the-money, and time value, everything above that. Intrinsic value does not decay; it is a function of where the underlying sits relative to the strike and changes only when the underlying moves. Time value is the part that pays for the chance that the option moves further into the money before expiry, and that chance shrinks with every passing day, so time value is what theta erodes.

This explains why theta varies with moneyness. A deep in-the-money option is almost all intrinsic value, with little time value to lose, so its theta is small relative to its premium. A deep out-of-the-money option has only a little time value to begin with, so its absolute theta is also modest. The at-the-money option carries the most time value of any strike, and so it carries the largest theta in rupee terms. The Varsity theta material uses the image of melting ice: an at-the-money option is the flat sheet with the most exposed surface, decaying fastest, while a small in-the-money option has less time value to lose. For how the intrinsic and time components split across the chain, see moneyness: in-the-money, at-the-money, out-of-the-money and option premium .

Option	Time value	Theta relative to premium
Deep in-the-money	Small, mostly intrinsic	Low
At-the-money	Largest	Highest in rupee terms
Deep out-of-the-money	Small	Low in rupee terms

Why theta accelerates near expiry

Time value must reach zero at expiry, but it does not run down in a straight line. The decay curve is shallow when months remain and steep in the final days, because the uncertainty that time value pays for collapses fastest right before the outcome is fixed. An at-the-money option with 45 days left loses only a little value per day; the same option in its final week loses a much larger fraction per day, and on expiry day the remaining time value bleeds out within hours.

The practical scale of this is large for weekly contracts. The time value in a weekly option with five days left can decay ten to twenty times faster per day, in proportion, than the time value in a monthly option with thirty days left on the same underlying. This is why short-dated premium selling looks attractive: the seller collects the fastest decay. It is also why short-dated buying is punishing: the buyer pays the fastest decay and needs a quick, favourable move to overcome it. The acceleration runs alongside the gamma spike near expiry, so the final-week writer earns rich theta but takes on sharp gamma risk at the same time; the two are the paired cost and benefit of holding short premium into expiry. See expiry-day options trading and weekly versus monthly expiry for the contract-level detail.

Why sellers are long theta and buyers short theta

The buyer-versus-writer asymmetry is the whole reason theta sits at the centre of option strategy. A buyer pays a premium for the right to a future payoff; every day that passes without a favourable move erodes the time value they paid for, so the buyer is short theta and loses to the clock. A writer receives that premium; every day of erosion is money kept, so the writer is long theta and the clock works for them.

A short at-the-money index straddle with a combined theta of, say, +500 rupees per day earns about 500 rupees a day in time value if the underlying and implied volatility stay put, the carry income of the position. A long call with theta of -200 rupees per day costs 200 rupees a day in decay, which a favourable move in the underlying must recover before the trade turns profitable. The asymmetry is not free money, because the theta a writer earns is the premium they collected for taking on the gamma and vega risk; in a calm market the theta wins, and in a sharp move or a volatility spike the writer’s collected theta is dwarfed by the loss. This is the structural reason most premium-selling strategies pair positive theta with negative gamma and negative vega. For the margin the exchange charges against that risk, see SPAN margin on Zerodha , exposure margin on Zerodha and naked option-selling margin on Zerodha .

Weekend and holiday decay

Theta accrues on every calendar day, not only on trading days. Time value pays for the chance of a move, and the calendar keeps counting down through Saturdays, Sundays and exchange holidays even though the market is shut. The consequence shows up at the Monday open: an option held across a weekend has lost three calendar days of time value, so its premium can open lower on Monday than its Friday close, purely from decay, even when the underlying gapped neither up nor down.

Most pricing models and the Kite display smooth this, spreading the decay across calendar days rather than dumping the weekend’s three days into Monday morning, so the holder often sees the weekend bleed reflected gradually rather than as a single Monday step. The effect is most visible on short-dated long options held over a long weekend with two market holidays attached, where four or five calendar days of decay land against a contract that had little time value to start with. A buyer planning to hold over a weekend should price in the calendar-day decay before entering; a writer holding short premium over a weekend collects it.

Theta against the other Greeks

Theta is only one side of a position, and reading it without its partners misleads. The daily decay a writer collects is the rent paid by the buyer for the convexity that gamma supplies, so positive theta and negative gamma almost always travel together on a short-premium book, and negative theta and positive gamma travel together on a long-premium book. A short straddle earns theta every quiet day and loses to gamma on the day the underlying moves sharply; the theta is the compensation for carrying that gamma risk. The two net out in the writer’s favour only when realised volatility stays below the implied volatility the premium priced.

Theta also interacts with vega around events. Implied volatility tends to rise into a scheduled event and collapse after, and a long-premium holder waiting through the run-up pays theta every day while hoping the eventual move or the volatility rise outpaces the accumulated decay. A trader who buys a weekly option a week before results pays the fastest theta in the contract’s life and then faces the post-event implied-volatility crush, so the position needs a large, quick move to overcome both. Varsity’s standing point holds: read the premium as the product of all the Greeks, since a high theta means nothing in isolation if the underlying gaps or implied volatility jumps. For the volatility leg, see vega and implied volatility ; for how this shapes which strike to pick, see strike selection on the option chain .

The asymmetry has a tax and cost dimension too. The theta a writer collects is gross; brokerage, STT and the bid-ask spread on entry and exit reduce it, and frequent re-striking to chase decay compounds those costs. F&O gains and losses are taxed as business income in India, so the net theta a writer keeps after costs and tax is smaller than the gross decay on the screen; see Zerodha F&O charges and F&O taxation in India .

Reading theta on Kite and using it

On Kite, the option chain’s Greeks tab shows theta per unit of the underlying for every call and put at every strike, computed from the Black-Scholes-Merton model. Multiply by the lot size for the position figure. For a multi-leg position, the net theta is the figure that matters, and Sensibull’s strategy builder displays it: a positive net theta marks a position that earns daily carry, a negative net theta marks one that pays it. A trader using theta deliberately sells time value when they expect a quiet, range-bound market and buys it only when they expect a move large or fast enough to beat the decay. Because theta is derived from the model’s implied volatility, an illiquid strike with a wide bid-ask spread produces a theta to be read as indicative only. For where the figure sits, see how to use the options chain on Kite and how to build an options strategy on Sensibull ; for the charges that eat into collected theta, see Zerodha F&O charges .

External references

References

Black, F. and Scholes, M. (1973). The Pricing of Options and Corporate Liabilities. Journal of Political Economy, 81(3), 637 to 654.
Hull, J.C. (2021). Options, Futures, and Other Derivatives (11th ed.). Pearson, chapters on the Greek letters.
Zerodha Varsity, Option Theory for Professional Trading, theta chapter (as of June 2026).
NSE, Equity Derivatives, contract specifications and education material, nseindia.com.
SEBI, Analysis of Profit and Loss of Individual Traders Dealing in Equity F&O Segment, January 2023 and the September 2024 update.

Frequently asked questions

What is theta in options?

Theta is the option Greek that measures how much premium an option loses for each calendar day that passes, holding the underlying price and volatility constant. It is the daily cost of time. A theta of -5 means the option loses about 5 rupees of premium per day from time alone.

Why are option sellers long theta and buyers short theta?

Time decay erodes premium, which helps the writer who collected it and hurts the buyer who paid it. So the seller is long theta, earning the decay each day, and the buyer is short theta, paying it. This is the core trade-off of option writing versus buying.

Why does theta accelerate near expiry?

An option’s time value must reach zero at expiry, and the curve is not linear. It decays slowly when months remain and fast in the final days, because the uncertainty that time value pays for collapses rapidly as expiry approaches. The last week decays far faster per day than the first.

Does theta apply over weekends?

Yes. Theta accrues on every calendar day, including weekends and exchange holidays. A long option held over a weekend loses three days of time value, so premiums can open lower on Monday morning purely from decay, even if the underlying has not moved.

Which options have the most theta?

At-the-money options carry the largest theta in rupee terms, because they hold the most time value to lose. Deep in-the-money options are mostly intrinsic value, which does not decay, so their theta is small relative to their premium. Theta is the price of time value.

How do I earn theta on Zerodha?

By writing options, where you collect premium that decays in your favour, or by running a net-short-premium strategy such as a credit spread whose net theta is positive. Sensibull shows the net theta of a multi-leg position. Writing carries margin and open-ended risk, so size it against the SEBI loss data.

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Last reviewed: 21 June 2026
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