IDX to Strip HSC Stocks From IHSG Index, 18% Weight at Stake

The Indonesia Stock Exchange (IDX) will remove all stocks classified as high shareholding concentration (HSC) from the calculation of the IHSG, the country's benchmark stock index. IDX President Director Jeffrey Hendrik announced the plan at a press conference at the IDX building on Monday, October 19, 2026.

"To provide a more credible and trustworthy price index, we will remove all high shareholding concentration stocks from the composite stock price index," Jeffrey said, as quoted by Kompas.com.

What Counts as an HSC Stock

HSC stands for high shareholding concentration, IDX's term for stocks whose ownership is controlled by a small group of investors. The fewer active shareholders trading a stock, the more prone it is to unusual price swings, since buy and sell orders can end up dominated by just a handful of parties.

Jeffrey said there is "potential risk" embedded in stocks with this kind of ownership structure. Still, IDX stressed the HSC label does not mean the issuer violated any capital market regulation. The classification is purely about ownership structure, not a legal breach.

18% of the Index, 80 Issuers Affected

IDX counted 80 listed companies falling under the HSC category as of this announcement. Combined, these stocks account for roughly 18% of the IHSG's weight, a sizable chunk given the IHSG is the main benchmark tracked daily by both retail and institutional investors.

With that much weight, price moves in a handful of HSC stocks can end up dragging the entire IHSG in one direction, even though actual market participation in those names is narrow. That is the core reason IDX decided to strip them from the headline index calculation.

Not a New Idea, Already Applied to Flagship Indices

This move is actually an extension of a rule already in place. HSC stocks have previously been excluded from, or simply never qualified for, several IDX flagship indices such as IDX30, LQ45, and IDX80. Those three indices are specifically designed to showcase the exchange's most liquid, large-cap names.

Jeffrey said going forward, all HSC stocks will also be removed from the IHSG calculation. IDX framed the move as part of a broader initiative to continue capital market reform in Indonesia.

Not a Delisting, Stocks Remain Tradable

Jeffrey was clear the policy is not a delisting or removal from the exchange's listing. HSC-classified stocks can still be bought and sold on IDX as usual. The difference is their price moves will no longer feed into the IHSG's calculation.

The goal, according to Jeffrey, is to give a more accurate picture of how the IHSG actually moves. Under the current setup, the index can swing sharply just because of a handful of thinly-held stocks, even when broader market participation does not reflect that move.

Why Index Transparency Matters Now

The IHSG is calculated using market-cap weighting, meaning the bigger a stock's market value, the more influence it has on the index's movement. The problem is that a large market cap does not always correspond to healthy liquidity or a broad shareholder base. An HSC stock can look large on paper while most of its shares simply change hands among a small circle of investors.

The IHSG serves as a reference point for many players: fund managers running index funds, analysts building macro forecasts, and retail investors reading daily market sentiment. If 18% of the index's weight is being driven by stocks with narrow ownership, the signal from IHSG movements can be misleading rather than reflecting genuine market conditions.

For passive index funds or products tracking the IHSG, this reshuffle also means portfolio adjustments once HSC stocks are officially stripped out. Stocks with wider shareholder distribution and more even liquidity will automatically see their index weight grow once HSC names are excluded.

What It Means for Investors

Investors holding HSC-classified stocks should watch for IDX's official list of the 80 issuers, since the status can affect market perception of a stock's liquidity even though it is not a legal violation. The stocks remain freely tradable on the exchange, so there is no requirement to exit positions.

For anyone using the IHSG as a benchmark for index funds or ETFs, it is worth tracking IDX's formal rule and effective date, since the index's weight composition could shift meaningfully once 18% of current weight is excluded.

One more thing worth noting for day traders: once HSC stocks are excluded from the calculation, future IHSG moves are likely to reflect broader market participation and become less susceptible to being pushed around by trading in narrowly-held names.

Scenarios to Watch

A few things are worth tracking in the coming weeks. First, the official effective date for this rule, since the available sources have not specified when implementation begins. Second, the full list of the 80 HSC issuers, which IDX has not publicly detailed in this announcement.

Third, the impact on sector weighting within the IHSG once 18% of market cap gets excluded from the calculation. A shift of that size could reshuffle sector dominance in the index, particularly if most HSC stocks are concentrated in a specific sector or business group.

What does HSC mean in Indonesian stocks?

High shareholding concentration (HSC) is IDX's term for stocks whose ownership is controlled by a small group of investors, making prices prone to unusual moves.

Are HSC stocks being delisted from IDX?

No. IDX says this is not a delisting. HSC stocks can still be traded, but their price moves will no longer count toward the IHSG index.

How many stocks fall under the HSC category?

As of October 19, 2026, IDX identified 80 listed companies as HSC stocks, together weighing around 18 percent of the IHSG.

When does this rule take effect?

The available sources do not specify an effective date. IDX only announced the plan at a press conference on October 19, 2026.