mumbai, Aug. 28 -- An increase in foreign institutional participation has resulted in non-expiry day volumes on BSE to increase sharply from fiscal year 2024-25 (FY25) to FY26, market experts said, citing the Securities and Exchange Board of India's (Sebi) recent study titled "profitability of individual traders in the equities derivatives segment FY25-FY26". The study, released earlier this month, examines both expiry and non-expiry average daily premium turnover over three periods-pre-policy tightening (April-October 2024), immediate post-policy (December 2024 -March 2025), and the recent period (October 2025-March 2026). The regulatory tightening refers to tripling contract size, rationalizing weekly expiries to one per exchange from multiple earlier and doubling the tail risk margin (extreme investment outcome risk) on expiry day, among others. Additionally, the government raised the securities transaction tax (STT) on futures and options, too, in October 2024. Regulatory curbs were rolled out in phases from November 2024 through March and December 2025 to tame the retail frenzy in options trading, leading to aggregate losses of Rs.1.8 trillion among retail traders over three years (FY22-24). Interestingly, the study found that BSE expiry day average daily turnover (ADT) jumped by 15.2% from Rs.22,271 crore pre-policy to Rs.25,648 crore in the immediate post-policy period. The non-expiry day ADT surged 528.4% to Rs.6,917 crore from Rs.1,101 crore. To be sure, the incremental percentage looks inflated as it is on a very low base. The expiry ADT of BSE stood at Rs.53,357 crore in the recent period. The non-expiry day ADT rose further to Rs.15,667 crore in the third period ending in FY26. Consequently, the BSE expiry to non-expiry ratio decreased sharply from 20.2 times pre-policy to 3.7 times immediate post-policy and to 3.4 times in the third period under review. In the case of the larger rival, NSE, the ratio remained the same at 1.1 times in the second period and increased to 1.6 times in the third period. This was because while the expiry day Nifty options ADT rose above the pre-policy average, the non-expiry ADT, while improving, stayed below the pre-policy average....