--- title: "What is theta decay, and how fast is it on expiry day?" description: "Theta is the amount an option loses each day from the passing of time alone, with the index and volatility held where they are." source_url: "https://www.rupeecase.com/learn/questions/theta-decay-on-expiry" --- At the money call theta grows as expiry nears, most of all in the last days Theta of the at the money NIFTY call on the 10 Jun 2026 chain, rupees per lot of 65 units per calendar day, drawn against the level of the future with twenty, ten and two days left. Expiry is 30 Jun 2026. Source: NSE end of day data, computed by RupeeCase. As of 10 Jun 2026. Take the NIFTY chain of 10 Jun 2026, expiry 30 Jun 2026. The at the money call loses value every day, even when the index does not move. That daily loss is theta: the change in an option's value from time alone, with the index and implied volatility held still. The chart shows that call's theta with twenty, ten and two days left. It is drawn against the level of the future, so the height shows the size of the daily loss, and the width shows how it fades as the index moves away from the strike. Read the height first, then the shape. The curve gets taller as expiry nears. With two days left, the daily loss of the at the money call is about three times what it was with twenty days left. The same time value is squeezed into fewer days, so more than half of the premium that was there with twenty days left is lost in the last week, if the index and volatility stand still. On the last day itself, whatever time value is left is gone by the close. At the final settlement an option is worth its intrinsic value, the gap between the index and the strike, or nothing. The expiry day rules are in module I25. Theta is a cost to the buyer and a gain to the seller while the index stays put. The seller keeps it only while the index stays on the right side of the strike. A large move against the position can cost more than many days of theta, which is the link to gamma. **Before you trade.** Derivatives trading carries a high risk of loss. SEBI's study "Profitability of Individual Traders in the Equity Derivatives Segment (FY25 to FY26)" (August 2026) found that 87.7% of individual traders in equity F&O made net losses in FY26, with aggregate net losses of Rs 91,685 crore. [Read the SEBI study](https://www.sebi.gov.in/reports-and-statistics/research/aug-2026/study-profitability-of-individual-traders-in-the-equity-derivatives-segment-fy25-fy26-_103835.html) What is theta decay, and how fast is it on expiry day?Theta is the amount an option loses each day from the passing of time alone, with the index and volatility held where they are. For an at the money option it grows as expiry gets close, and by the final settlement the time value has gone, so only intrinsic value is left. LGo deeper ## Where Learn teaches this. [Go deeperTheta: the time decay curve into expiry7 min, Beginner](/learn/path-14/module-14-8-theta-time-decay)[Go deeperExpiry day: gamma, theta, settlement and the rules10 min, Intermediate](/learn/path-17/module-17-12-expiry-day)[Try itGreeks calculatorDelta to rho, and vanna to colour in expert mode, from one Black 76 engine.](/learn/tools/greeks-calculator) SSources ## Go to the source. 3 sources, Book the most cited The publisher of each source listed below. Source: Module undefined source list. 1. [NSE, equity derivatives contract specifications (expiry cycle, lot size, settlement)](https://www.nseindia.com/static/products-services/equity-derivatives-contract-specifications) NSE 2. [SEBI investor education, Understanding derivatives](https://investor.sebi.gov.in/understanding_derivatives.html) SEBI 3. Hull, John C., Options, Futures, and Other Derivatives (textbook, chapters on Greeks and time value) Book ?Questions people ask ## Related questions. 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