What the Sensex Measures
The Sensitive Index, launched on January 1, 1986 with a base of 100 pinned to 1978-79, tracks thirty of the largest and most liquid companies listed on the BSE. It is the number Indian evening bulletins read out first, and for four decades it has served as shorthand for Indian equities the way the Dow Jones industrial average does for America. Thirty names cannot represent five thousand listings, but they capture where the bulk of institutional money actually sits.
Weighting matters as much as membership. Because the index is float market-cap weighted, a 5 percent move in Reliance shifts the Sensex by well over a hundred points on its own, while the smallest constituent needs a near-circuit move to register. Reading the index means reading its biggest names first.
The Constituents and Sector Spread
Membership rolls with the economy. Recent compositions carried Reliance Industries at the top weight, ICICI Bank and HDFC Bank close behind, then TCS, Infosys, Bharti Airtel, Larsen and Toubro, ITC, State Bank of India and Kotak Mahindra. Financials dominate at roughly a third of the index, information technology takes about a fifth, and oil and gas, consumer staples, autos and power share the remainder. When bank earnings season disappoints, the Sensex feels it no matter what mid caps are doing.
Free-Float Methodology
Since September 2003 the index has been weighted by free-float market capitalization, counting only shares genuinely available to the public rather than total market value. A promoter family holding 75 percent of a giant contributes just the float slice to index weight. The method matters because index funds must replicate these weights exactly, so free-float changes drive passive buying and selling mechanically, and tightly floated favorites can trade at premiums that full market-cap math would never justify.
Family-controlled conglomerates illustrate the difference sharply. The same economic footprint can carry very different index weight depending on how much equity the promoter group actually holds, which is one reason the Sensex and older full market-cap measures occasionally disagree on leadership.
Rebalancing Twice a Year
The exchange reviews constituents every June and December, dropping names that slip in liquidity, float or listing standards and promoting the qualified replacements. Changes are announced weeks in advance and implemented with buffers so index funds can migrate without shocking prices. Inclusion is an event in itself: a stock entering the Sensex enjoys a visible stretch of passive accumulation, which is why speculation about candidates trades actively before each announcement.
Long-Run Returns
From its late-1970s base the Sensex has compounded near 12 to 14 percent annually in price terms, higher with dividends, despite wars, devaluations and repeated 40 percent drawdowns. It first closed above 10,000 in February 2006, crossed 50,000 in January 2021 and touched 80,000 on July 3, 2024, before corrections reminded everyone that averages are earned through pain. Dividends deserve respect too: the total return variant, reinvesting payouts, has added meaningfully over forty years, and that gap compounds exactly like everything else in this business. The route was never smooth: the index lost more than half in calendar 2008, needed until late 2010 to durably reclaim its January 2008 peak, and dropped 38 percent in early 2020 before recovering within ten months. Investors who added during those breaks rather than exiting captured returns well above the long-run average.
Trading the Sensex on ErawanEx
On ErawanEx you can track Sensex futures alongside cash equities, with lot values and margin notes shown before order entry so exposure is sized deliberately. ErawanEx users hedging concentrated stock books commonly short index futures to cut beta without selling winners into weakness. The platform also carries the total return version of the index for comparison, which adds roughly a percent a year of dividends to the price line. The index rewards patience, punishes leverage, and pays those who respect both, in exactly that order.