Generally, when a listed company operates and generates profits, it often returns value to shareholders through regular dividends or sometimes special dividends. Additionally, dividends may be issued in the form of shares. Occasionally, if the company needs additional capital, it may announce a capital increase to raise funds.
For ordinary stock investors, the above events are common occurrences.
However, for trading Single Stock Futures (SSF), these rights are not granted. Some Corporate Actions can also affect Futures holders. Therefore, to ensure fairness among Futures holders, the TFEX market adjusts contracts to prevent any advantage or disadvantage between contracting parties.
Corporate Action (CA) refers to events undertaken by a listed company that affect its common shares, which consequently impact the underlying stocks of Single Stock Futures.
Therefore, the Thailand Futures Exchange (TFEX) adjusts Single Stock Futures contracts so that holders' positions are not adversely affected by such changes. (Regular dividend payments do not trigger contract adjustments by TFEX.)
Events that prompt TFEX to adjust contracts include:
For example, suppose PTT announces a change in its par value from 1 baht to 0.10 baht per share, effectively converting each old share into 10 new shares, effective 28 Apr 2026 GMT+7. On 27 Apr 2026 GMT+7, PTT's stock price is 400 baht and PTT Futures is also 400 baht.
After the par value change, theoretically, PTT's stock price on 28 Apr 2026 GMT+7 would adjust down from 400 baht to 40 baht. If someone held a Long position in PTT Futures at 400 baht on 27 Apr 2026 GMT+7, without contract adjustment, they would face significant losses due to the underlying stock's price drop.
Contract adjustments are made by calculating an Adjustment Factor (AF) to modify both the contract price and size. For par value changes, the calculation formula is as follows.
Calculating AF for changes in the par value of common shares.
AF = Number of old shares / Number of new shares.
For PTT's par value change, AF = 1 / 10 = 0.1.
Adjusted contract price = Original contract price × AF = 400 × 0.1 = 40 baht.
Adjusted contract size = Original contract size ÷ AF = 1,000 ÷ 0.1 = 10,000 shares.
Additionally, TFEX appends a letter suffix to the original contract symbol to indicate that the contract has been adjusted due to Corporate Action, starting with X. If further Corporate Actions occur on an already adjusted contract, suffixes Y and Z are used sequentially.
The result of these adjustments is that PTT Futures price on 28 Apr 2026 GMT+7 aligns with the adjusted underlying stock price of 40 baht, ensuring no advantage or disadvantage to either Long or Short Futures holders caused by the par value change.
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