Thailand Sets November 16, 2026 Start for Eight Trading Rule Changes

Smaller price steps, targeted fees and fewer trading restrictions

The Stock Exchange of Thailand (SET) will introduce eight revised trading measures on November 16, 2026, combining smaller price increments for shares priced from 5 to 50 baht with tighter controls on heavy order traffic and changes to short selling. Three existing restrictions will be removed: individual security Dynamic Price Bands, limits on which securities high frequency traders can trade, and minimum periods for keeping orders in the system.

The new order fee has three key thresholds. Accounts must have an order to trade ratio above 50 and submit an average of more than 50 orders per minute. For accounts meeting those conditions, the exchange will charge 0.15 baht per order only on the portion exceeding 15,000 orders a day. The fee is therefore not a blanket charge on automated trading.

Short selling will normally be permitted at a price equal to or above the latest traded price. If a security closes at least 10% below its previous closing price, short sales on the next trading day must instead be priced above the latest trade.

SET president Asadej Kongsiri said the package follows consultation with investors and other market participants in May and approval by Thailand's Securities and Exchange Commission (SEC). The exchange describes its aim as balancing liquidity and stability, reducing investor costs and supervising actual trading behavior. The November date uses the Gregorian calendar; the Thai announcement gives the year as 2569 in the Buddhist calendar.

A separate change taking effect on the same date will move the morning opening for derivative warrants and exchange traded funds linked to foreign securities to 8 am, two hours earlier than before. Closing times will remain unchanged.

What smaller price increments could change

The tick size is the smallest permitted step between order prices. Reducing it for shares priced between 5 and 50 baht will allow buyers and sellers to submit prices closer together. The exchange expects this to narrow the gap between the highest buying price and lowest selling price, known as the bid and ask spread, and improve the chances of matching orders.

That spread is a trading cost distinct from a broker's commission. An investor seeking immediate execution generally buys at the available selling price or sells at the available buying price. A narrower gap can reduce that cost, although the actual spread also depends on how many participants are willing to trade and how much stock they offer.

The change provides more pricing choices rather than a guarantee of cheaper execution. The announcement does not specify the complete revised tick size schedule, so it does not support a precise calculation of savings for any particular share. It also gives no measured forecast for the increase in liquidity.

Short selling gets a trigger tied to closing prices

Short selling involves selling borrowed securities, usually with the intention of buying them back later. Under the revised normal pricing rule, called Zero Plus Tick, the sale price must be equal to or higher than the latest traded price. The stricter Uptick rule requires a price above the latest trade.

The distinction matters when a share is under pressure. If its closing price falls by 10% or more compared with the previous day's close, the stricter requirement applies on the next trading day. It restricts the prices at which short sellers can execute without banning short selling in that security altogether.

The closing price test and the next trading day timing are important changes from an earlier proposal. That proposal described a fall of at least 10% from the previous close as triggering an Uptick restriction for the remainder of the same session. The announced package instead uses the closing decline to determine the rule for the following trading day.

Which securities will remain eligible for short sales?

Short selling will be limited to specified groups that the exchange identifies as sufficiently liquid: SET100 constituents, shares underlying Single Stock Futures, depositary receipts (DRs) and exchange traded funds (ETFs). Liquidity refers to the ability to buy or sell without causing a large price movement.

Single Stock Futures are contracts based on individual shares. DRs provide exposure to foreign securities through instruments traded locally, while ETFs are funds whose units trade on an exchange. Their inclusion means the revised eligible categories extend beyond the shares in the SET100 index.

An earlier proposal also described prohibiting short selling in securities underlying ETFs and derivative warrants. That restriction concerned the underlying securities, not necessarily the ETF units themselves. The final announcement summaries list the eligible groups but do not repeat that separate prohibition, so its precise treatment needs to be checked against the operative rules.

The removal of restrictions on what high frequency traders may buy and sell does not remove short selling requirements. Access to a security for ordinary trading and permission to sell it short are separate matters.

Registration will focus on how traders operate

The exchange is revising the characteristics that require traders to register for supervision. Relevant factors include use of a Dedicated API, order frequency and speed, positions remaining at the end of the day, and daily trading value. An API is a software connection through which a trading system can send orders directly through an authorized channel.

High frequency trading (HFT) uses automated systems to submit and manage orders rapidly. The revised approach looks beyond that label to observable activity. A trader sending many fast orders, generating substantial trading value and retaining little stock at the close may show the behavior the exchange intends to monitor.

Rongrak Panavudhi, SET senior executive vice president, described the proposed classification approach in terms of actual trading behavior, including order frequency, trading velocity, outstanding positions and daily value. The announced registration criteria follow that direction, although numerical cutoffs for each behavioral measure are not specified in the announcement.

Registration and the order fee are separate controls. A trader may need to register without meeting the conditions for an extra charge. Likewise, the fee is described in terms of account activity rather than simply whether an account is labeled HFT.

How the extra order fee works

The order to trade ratio (OTR) compares the number of orders submitted with the number of completed trades. A high ratio indicates substantial order traffic relative to successful execution. The exchange says the extra charge is intended to reflect the use of trading system resources and discourage orders submitted without an intention to obtain a match.

Under the announced thresholds, both an OTR above 50 and an average rate above 50 orders per minute must be met. The charge then applies only to orders beyond 15,000 per day, at 0.15 baht each. Merely sending more than 15,000 orders does not, by itself, establish that the fee is payable.

For illustration, an account that meets both activity conditions and submits 20,000 chargeable orders under the daily counting rules would have 5,000 orders above the allowance. Multiplying 5,000 by 0.15 baht gives an extra charge of 750 baht. This is a calculation from the announced thresholds, not a reported account charge.

The earlier proposal used an OTR above 100, more than 50 orders per active minute and a daily allowance of 30,000 orders. The announced OTR threshold and daily allowance are each half those proposed levels, while the rate remains 0.15 baht. Reports also differ in describing the minute measure: the proposal explicitly referred to an active minute, while the announcement summaries refer to an average per minute. The detailed calculation method matters for implementation.

Three restrictions will be removed

The first cancellation concerns Dynamic Price Bands for individual securities. These bands limit how far a security's price can move within a specified period. The exchange says removing them will reduce trading obstacles, particularly for shares with low liquidity. Smaller companies may also gain more trading flexibility, although no quantified effect is given.

The second removes restrictions on which securities HFT participants can trade. An earlier policy account described limiting these traders to SET100 shares. The revised package instead seeks to give them access across security types on the same basis as other investors, subject to the rules governing each activity.

The third removes Minimum Resting Time, the requirement that an order remain in the system for a minimum period before cancellation or amendment. The exchange expects this to improve order management and reduce the operational burden on member brokers.

An earlier proposal described replacing minimum resting time with surveillance using artificial intelligence to detect unusual trading patterns in real time. The final announcement summaries confirm the cancellation but do not give a deployment date or technical details for that surveillance. The broader shift is toward monitoring behavior and charging for qualifying order traffic while removing several direct trading restrictions.

A separate opening change for foreign linked products

From November 16, morning trading in derivative warrants and ETFs linked to foreign securities will begin at 8 am rather than 10 am. With closing times unchanged, the adjustment adds two hours at the start of their trading day.

Derivative warrants are instruments whose value depends on an underlying asset and whose terms determine the exposure they provide. The earlier opening applies to the specified products linked to foreign securities. It should not be read as a change to the opening time for all Thai shares.

This scheduling change is separate from the eight measures governing order pricing, short selling and automated activity. Investors trading these products therefore face both a timetable adjustment and any applicable changes to trading rules, rather than a single marketwide extension of hours.

How the policy moved from tighter curbs to a broader reset

The November package follows an earlier push for stricter limits during a period of weak market performance. On February 19, 2025, Asadej described plans to restrict short selling and HFT to SET100 shares, with implementation then expected in the second quarter after consultation and SEC approval.

At that time, foreign investors had withdrawn about US$10 billion over the preceding two years, and the SET index had fallen about 10% that year. Short selling since August 19 was valued at approximately 240 billion baht, about 4% of turnover. Those are historical figures, not measurements of market conditions at the November 2026 launch.

During discussion of the later proposed overhaul, Asadej, the SET president, described the intended balance between trading access and volatility controls:

"This roadmap will help create a more balanced trading environment and provide more concrete mechanisms to manage market volatility," he said.

The sequence shows why earlier proposals should not be treated as the final requirements:

• February 19, 2025: Plans for tighter SET100 limits were described, with implementation then expected in the second quarter.
• May 13 to 29: A subsequent overhaul proposal scheduled public hearings before submission to the SEC. Its fee thresholds and short selling trigger differed from the announced package.
• October 10, 2026: Reports described the approved rules and the separate opening time change following exchange filings.
• November 16, 2026: The eight revised measures and earlier opening for specified foreign linked products are scheduled to take effect.

The exchange directs investors to its rules and supervision area and trading related circulars for the detailed requirements. Outstanding practical details include the full tick size table, order counting conventions and behavioral registration thresholds. No measured results yet establish whether the changes will reduce spreads, improve matching or limit unusual price movements.

Key Points

• Eight revised SET trading measures take effect on November 16, 2026, after consultation and SEC approval.
• Shares priced from 5 to 50 baht will trade in smaller price increments.
• A closing decline of at least 10% triggers stricter short sale pricing on the next trading day.
• Short selling remains limited to SET100 shares, Single Stock Futures underlying shares, DRs and ETFs.
• Qualifying accounts face a 0.15 baht charge per order above 15,000 daily orders, subject to both OTR and order frequency conditions.
• Dynamic Price Bands, HFT security restrictions and Minimum Resting Time will be removed.
• Specified derivative warrants and ETFs linked to foreign securities will open at 8 am, with closing times unchanged.