The IDX's Opening Price Isn't Set the Moment the Market Opens. It's Set a Few Minutes Before, and Here's How
5 min read
Loading...
5 min read
You check a stock at 08:50. Yesterday it closed at Rp1,000. At 09:00 the market opens, and the first price on your screen is Rp1,060. Nobody traded at Rp1,060 yesterday. So where did that price come from?
It came from the IDX pre-opening session. This is a short window before trading starts where orders pile up, and the exchange picks one opening price for all of them at once.
The pre-opening session runs from 08:45 to 08:59:59 on trading days, according to Bisnis.com's report on the session schedule and Ajaib's explainer on pre-opening trades. Regular trading starts at 09:00.
It has two parts:
The reference price during this window is the previous day's closing price, per Ajaib.
The system looks for the price at which the most shares can change hands. That price becomes the opening price, according to the same Ajaib explainer.
Here is a made-up example. It is an illustration, not real market data.
| Price | Shares buyers would pay this much or more | Shares sellers would accept this much or less | Shares that can trade |
|---|---|---|---|
| Rp1,040 | 8,000 | 3,000 | 3,000 |
| Rp1,050 | 6,000 | 5,000 | 5,000 |
| Rp1,060 | 4,500 | 6,500 | 4,500 |
At Rp1,050, 5,000 shares can trade. That is more than at any other price, so Rp1,050 becomes the opening price. Everyone who matched trades at that same price, whether they bid Rp1,050 or Rp1,060.
Yesterday's close is only the starting reference. Overnight, news can arrive. US markets can move. A company can publish results after the close.
Investors send new orders based on that. If many more people want to buy than sell, the price that clears the most volume sits higher than yesterday's close. That is a gap up. If sellers dominate, it is a gap down.
You can see this on the price chart. A gap is a jump between one day's close and the next day's open, with no trades in between. To look at real recent prices, open the NetWort Market page or a stock like BBCA.
This used to be narrow. From 7 September 2020, only stocks in the LQ45 index (the 45 most liquid large IDX stocks) joined pre-opening, per Bisnis.com.
That changed on 9 December 2024. Under IDX Directors' Decision Kep-00196/BEI/12-2024, stocks on the Main Board, New Economy Board and Development Board can now trade in pre-opening, according to IDX Channel's report. Check with your broker whether a specific stock is included.
Here is a trick that used to exist. Someone posts a huge buy order to make the indicated price look high. Then they cancel it in the last seconds, before it can be matched. This is called spoofing.
Since 15 December 2025, IDX has a non-cancellation period to stop this. In pre-opening it starts at 08:56. During it, you cannot change or withdraw orders that are already in. You can still send new ones. The same rule applies before the close, starting at 15:56. This is according to Kontan and CNBC Indonesia.
Reports differ on exactly when the restriction ends, so confirm the details with your broker before relying on them.
Orders that are not matched in pre-opening move into the first trading session, unless their price is beyond the auto reject limit, according to one of the sources above. Auto reject is the daily cap on how far a price can move. We explain it in our guide to IDX auto reject.
Your place in the queue still follows the rules in how IDX matches orders by price and time. Price ticks follow the IDX tick size rules.
Do not treat the pre-opening price as a promise about the day. It is a snapshot of who sent orders in a few minutes. It can move away fast once regular trading starts.
Next time you see a stock open far from yesterday's close, open the NetWort Market page and look at how the broader market is moving that day. That helps you tell whether the gap was about one stock or about everything.