BSE could stand to lose market share in its largest revenue-generating segment after market regulator Securities and Exchange Board of India announced a change in expiry day for derivative contracts.SEBI announced Thursday as the revised expiry day for BSE's derivative contracts, with NSE being allotted Tuesday.The move could result in a 13% decline in index options' average daily premium for BSE, which could lead to an 8% cut in earnings estimates, Goldman Sachs said in a note dated June 16.Income generated from facilitating index option trades make up for nearly 60% of revenues for BSE, per the global brokerage.Expiry Swap: BSE F&O Expiry Shifts To Thursday After NSE Gets Tuesday NodBSE's market share in index options stood at 41% on Tuesdays, with the second day of the week accounting for 24% of the total volume traded during the week, based on premium turnover.!function(){"use strict";window.addEventListener("message",(function(a){if(void 0!==a.data["datawrapper-height"]){var e=document.querySelectorAll("iframe");for(var t in a.data["datawrapper-height"])for(var r,i=0;r=e[i];i++)if(r.contentWindow===a.source){var d=a.data["datawrapper-height"][t]+"px";r.style.height=d}}}))}();With the revision in expiry day, this could come down to 8%, according to Goldman Sachs, but with the share on Thursday rising to 41%, which currently stands at 8%.In October, the market regulator had released revised guidelines for rationalisation of index option contracts, limiting the number of weekly expiry of contracts to one per exchange.As a result of this limitation, combined with the new expiry day, and a renewed focus in capturing India's booming derivatives market, BSE's market share in weekly options had grown to 24% in May 2025, based on average daily premium, according to a Goldman Sachs note.But with the third revision in expiry day, BSE could stand to lose market share by 3 percentage points, which it had grown to 24% in May from near 0% in May 2023, per Goldman Sachs' analysis.This is the third change in expiry day for BSE in recent history. In August 2023, India's oldest exchange had announced a shift in expiry day for Sensex contracts to Friday, which were later changed to Tuesday in November 2024.Nifty F&O Expiry Shift To Tuesday A Significant Boost For Hedging: NSE's Sriram Krishnan. Read more on Markets by NDTV Profit.