Thailand Sets ISSB Reporting Timeline for Listed Companies

Thailand’s new sustainability reporting rules put listed companies on a staged path to disclosures aligned with the ISSB standards. The first reports are due in 2028 and will cover 2027 data, starting with the largest companies before the requirements extend across the market through 2031. That gap between the reporting year and publication gives companies time to prepare, but it also means the first disclosures will describe activity that has already happened. Investors and other readers will need to judge both what companies report and how clearly they explain their methods.

The policy marks a change in how companies are expected to organize sustainability information. Reporting under multiple frameworks can leave readers comparing disclosures built for different purposes and with different definitions. An ISSB-aligned approach offers a common reference point, though a shared framework can't by itself ensure that companies collect equally detailed or reliable data.

A phased schedule for the market

SET50 companies will report under the new rules first, in 2028. SET100 companies follow in 2029, then all other companies listed on the Stock Exchange of Thailand in 2030. In 2031, the requirements extend to companies on the mai exchange, along with REITs, IFFs, IFTs and PFs. The sequence gives larger listed companies the earliest reporting obligation, then brings a wider set of entities into scope over several years.

For companies, the schedule makes timing a practical planning issue. Teams will need to work out which information they can already support, where records are incomplete, and who across the business is responsible for supplying data. Sustainability reporting often draws on information held in different parts of an organization; gathering it consistently can require changes to internal processes, even when the underlying activity is familiar. The staged dates give companies time to make those changes, but the preparation period still has to produce information suitable for formal disclosure.

The order also matters to readers. Early reports from the largest companies may help investors understand how the rules are being applied, while later filings will bring in companies with different operations and reporting capacity. That makes consistency a test over time: a common standard is useful only if disclosures remain intelligible as the pool of reporting companies expands.

Assurance, data and transition relief

Greenhouse gas emissions disclosures must be verified by assurance providers using internationally accepted assurance standards. That requirement puts the quality and traceability of emissions data in focus. A company needs more than a headline figure: it must be able to explain how the figure was assembled and support it with records that an assurance provider can examine. The rules establish a verification expectation, while the work of building dependable data processes will sit with the companies reporting.

The regulations also offer transition reliefs, including a first-year exemption from comparative information, flexibility in reporting timelines, permission to use equivalent emissions calculation standards, and an initial exemption from Scope 3 disclosures. These measures acknowledge that companies may need time to establish reporting systems and obtain information. They can ease the first reporting cycle, though they also mean early reports may not provide the same breadth of detail across every company.

Scope 3 emissions can involve activity beyond a company’s direct operations, making the relevant information harder to gather. An initial exemption gives companies room to develop the processes needed for that reporting. It also leaves readers with an early limitation: they may not yet see a complete account of emissions associated with a company’s wider value chain. That distinction should be visible in how the first reports are read.

Here’s the thing: a transition period is useful only if it leads somewhere. The exemptions and flexibilities can give companies time to improve their methods, but the reports will need to make clear what has been measured, what remains unavailable, and which calculation choices were used. Otherwise, readers may struggle to tell the difference between genuine progress and a disclosure that is simply easier to produce.

From flexible frameworks to ISSB alignment

Since 2022, Thailand’s Securities and Exchange Commission has required listed companies to report on ESG performance, governance, human rights and emissions in their annual filings. Companies could choose among external frameworks, including the Global Reporting Initiative Standards and TCFD recommendations. That flexibility gave companies options for organizing information, but it also meant that disclosures could vary in structure and emphasis.

After consulting on a shift in 2024, the SEC has adopted the ISSB approach to support international alignment and improve comparability. The ISSB published its first sustainability and climate standards, IFRS S1 and IFRS S2, in June 2023; more than 45 jurisdictions have since begun the process of using them. That broader uptake gives Thailand’s decision an international context, although adopting a standard doesn't guarantee that every market will apply it in precisely the same way.

The shift is more significant than it looks. Moving from a choice of frameworks toward a shared basis can make it easier for investors to compare information across companies, especially when they assess climate-related risks and broader sustainability matters. Yet comparability depends on execution: definitions, data quality and explanations of assumptions all affect whether two disclosures can be read side by side.

What the first reporting cycles will show

The phase-in and reliefs give companies time to build reporting systems and data capabilities. The practical test will be whether those preparations produce emissions and sustainability disclosures that investors can compare across Thai companies. Readers should expect the early reports to reveal not only company performance, but also how prepared organizations are to measure and explain it.

If you're working in this space, the useful question isn't just whether a company has published a report. Look at how it describes its methods, the limits of its data and the work still needed to meet the requirements. (And this is the part most people overlook.) A polished disclosure can still leave important gaps if its figures can't be compared or traced to a clear process.

Thailand’s staged timetable creates a sequence in which reporting practices will develop across different groups of companies. The first filings will offer an early view of what the new approach can deliver; later rounds will show whether the common framework produces disclosures that are both more consistent and more useful. A long runway. The standard sets a direction, but the credibility of the result will depend on the information companies can substantiate.