Delta Decay

Delta Decay refers to the gradual reduction in an option's delta as time passes and the option approaches its expiry date — a phenomenon most pronounced for at-the-money options. As expiry approaches, the probability that an at-the-money option will expire in the money converges toward 50%, but the sensitivity of the option price to small moves in the underlying diminishes rapidly in the final days and hours of the contract's life. Delta decay is closely related to the acceleration of theta decay near expiry and is most visible in short-dated weekly options on Nifty 50 and Bank Nifty traded on NSE. For options sellers in India who use short-dated OTM option-selling strategies, understanding delta decay is important because it affects how quickly their positions become 'immune' to small adverse price moves as expiry nears. For options buyers, delta decay means that even a correct directional bet generates diminishing returns as the option loses its price sensitivity in the final hours before expiry.