Trading More Often Has a Real, Measurable Cost Even Before Fees: The Bid-Ask Spread
6 min read
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6 min read
You check your trade and the numbers look clean: buy price, sell price, one small commission line. But there's another cost baked into almost every trade you place on the IDX, and it never shows up as a separate line item on your statement. It's called the bid-ask spread. On a heavily traded stock like Bank Central Asia (BBCA), it's small, under half a percent. On a thinly traded lapis dua stock, that same cost can eat more than 7% of your trade, before a single rupiah of commission is charged.
Every stock on the exchange has two prices quoted at once: the bid, the highest price someone is currently willing to pay to buy it, and the ask (or offer), the lowest price someone is currently willing to sell it for. The gap between those two numbers is the spread. If you need to buy right now, you pay the ask. If you need to sell right now, you receive the bid. Buy and then immediately sell the same share, even if the price hasn't moved at all, and you still come out behind by the width of that gap. That's a real, measurable cost, and it's completely separate from whatever commission your broker charges.
The exchange doesn't let bid and ask prices sit at just any two numbers. Under IDX's own trading rule, Peraturan Nomor II-A (the tick-size bands were set in Kep-00023/BEI/04-2016 and remain in force under the March 2023 update, Kep-00055/BEI/03-2023), every stock's price can only move in fixed steps called fraksi harga, or price fraction, and the step size grows as the stock's price does:
| Price band | Minimum tick (fraksi harga) |
|---|---|
| Below Rp200 | Rp1 |
| Rp200 to Rp500 | Rp2 |
| Rp500 to Rp2,000 | Rp5 |
| Rp2,000 to Rp5,000 | Rp10 |
| Rp5,000 and above | Rp25 |
That table sets the tightest a spread can legally be: exactly one tick, if a buyer and a seller happen to be lined up at two adjacent price levels. No stock can trade at a bid and ask any closer together than that, no matter how liquid it is.
BBCA, the largest company on the IDX by market value, traded around Rp6,300 a share on 14 August 2026 (Fortune Indonesia). At that price, BBCA sits in the top price band, so its tick is Rp25. If BBCA's order book is as tight as the rule allows, say a bid at Rp6,275 sitting right against an ask at Rp6,300, buying at the ask and immediately selling at the bid costs Rp25 a share, about 0.4% of the trade (Rp25 divided by Rp6,300). On Rp10,000,000 invested, that's roughly Rp40,000 gone to the spread alone, before any commission.
BBCA is one of the most actively traded stocks on the exchange, so in practice its real spread usually does sit at or close to that one-tick minimum. With so many buy and sell orders queued at nearly every price level, there's rarely a gap wider than one tick between the best bid and the best ask.
Plenty of IDX-listed companies trade far less often than BBCA does, and a lower price band changes the math directly. Receh.in's own July 2026 roundup of Indonesia's cheapest listed stocks found Waskita Beton Precast (WSBP) at Rp14 as of 22 July 2026, trading in the under-Rp200 band where the minimum tick is just Rp1.
One rupiah sounds tiny, but measured against a Rp14 share price, it isn't: Rp1 divided by Rp14 works out to about 7.1%. That's the minimum possible spread on a stock at that price, roughly eighteen times wider than BBCA's 0.4% floor, purely because of where the price sits on the tick-size table. On the same Rp10,000,000 invested, a round trip at that minimum spread would cost around Rp710,000 on WSBP, against roughly Rp40,000 on BBCA.
IDX itself treats wide spreads on illiquid stocks as a real market-quality problem: in May 2025 the exchange introduced a formal Liquidity Provider scheme specifically aimed at narrowing spreads on thinly traded names (Bareksa).
None of this replaces your broker's commission, it adds to it. Two of Indonesia's larger retail brokers, Ajaib and Stockbit Sekuritas, both charge around 0.15% to buy and 0.25% to sell as of 2026 (Ajaib, Stockbit Sekuritas Help Center), on top of the exchange's own IDX, KPEI and KSEI transaction levy (about 0.0433%), 11% VAT charged on the commission itself, and a 0.1% final income tax on the sell side, all four figures independently verified against securities firms' own published rates as of May 2026 (Rankia.id). A full round trip on a liquid stock like BBCA can add roughly 0.5% to 0.6% in commission-related costs on top of that 0.4% spread. On a thin lapis dua name, the same commission structure sits on top of a spread several times larger, and the real spread, not just the minimum, can be wider still.
A single long-term buy, held until it's eventually sold, only pays the spread twice: once going in, once coming out. Someone actively trading the same rupiah in and out of a stock several times a month pays it every single round trip, on top of commission every single time. On a liquid name like BBCA, that cost stays manageable. On a thinly traded lapis dua stock, frequent trading turns a spread most investors never think about into one of the largest costs in the whole strategy, often bigger than the commission sitting right next to it.
Before trading a stock you don't already hold, check how actively it trades. NetWort's BBCA asset page shows the kind of liquid, closely-quoted name where the spread stays tight, and your Portfolio Health view is where to see how much recent trading activity has actually cost you, spread and commission both, against simply holding.