Direct Answer
The SET50 Index is a rule-based measurement of Thai blue-chip equity benchmark, maintained by Stock Exchange of Thailand. Like every index it owns nothing: it is a number produced by applying a published weighting formula to a selected list of companies, revised on a schedule the provider sets.
What this index covers
The SET50 Index covers Thai blue-chip equity benchmark, within the Thailand market. Stock Exchange of Thailand defines which securities are eligible, how they are selected from that pool, and how much each one contributes to the published number.
The name states a target of 50 companies. A target is not a guarantee of the exact count on any given day: corporate actions, dual share classes and pending additions all move the real number around it.
How constituents are weighted
Market capitalization weighted using listed shares, with each constituent capped at a maximum weight of 10 percent, adjusted quarterly. The separate SET50FF variant adds a free float factor and keeps the same cap.
The weighting method is the single biggest driver of how an index behaves. Two indexes covering the same market can diverge for years purely because they weight differently, which is why comparing index levels without knowing the method tells you very little.
What qualifies for inclusion
Common stocks of Thai companies, or foreign companies listed only on SET, traded in baht. Property funds, REITs and infrastructure funds are excluded. A security needs at least 20 percent free float and no bankruptcy, debt default, adverse audit opinion or delisting process. The 200 largest by market cap are reviewed, and the 50 largest that pass liquidity tests are selected.
Eligibility rules are the part of an index most readers never look at and the part that decides what it can possibly measure. A screen that excludes a whole sector, or admits only one listing venue, shapes the result far more than any day of trading does.
How long a listing must exist first
A security must have been listed at least 6 months, and one returning from a long suspension must have resumed trading at least 6 months earlier. Liquidity needs monthly trading value of at least 25% of the average per security value and monthly volume of at least 1% of registered shares, in at least 3 of 4 trading months.
A seasoning rule is why a large new listing does not appear in an index the week it starts trading. It is a deliberate lag, and it means an index can under-represent a fast-growing part of the market for months at a time.
When the membership is revised
Reviewed twice a year, with changes effective in January using data to the end of November and in July using data to the end of May. Between reviews, constituents can change for events such as delisting, suspension or mergers, and capped weights are adjusted quarterly.
Reconstitution is the one date an index changes shape by design rather than by price. Funds tracking it have to trade toward the new membership, which is why the schedule matters to anyone holding the tracker rather than only to the provider.
The rule that surprises people
The plain SET50 is not free float adjusted. Only the SET50FF variant adds the free float factor, and reserve securities are those ranked 51st to 100th by market capitalization.
References
- Stock Exchange of Thailand: Stock Exchange of Thailand Ground Rules for SET Index Series, as published 2026. Every rule described on this page is taken from this document.
Current SET50 Index constituents
Stock Exchange of Thailand publishes and licenses the SET50 Index constituent list. Swoopr does not republish it here. The provider's own page is the authoritative source for current membership and weights.
Related reading
- All stock market indexes: how indexes are built, weighted and revised.
- Emerging Markets indexes: others covering the same region.
- Index concentration: measuring how much of an index sits in its largest holdings.
- Index rebalancing and inclusion effects: what happens to a stock when index membership changes.
Frequently Asked Questions
Who maintains the SET50 Index?
Stock Exchange of Thailand maintains the SET50 Index and publishes the methodology document that defines its eligibility and weighting rules.
What does the SET50 Index measure?
It measures Thai blue-chip equity benchmark. The index is a calculated number applying a weighting formula to a selected list of companies, and it holds nothing itself.
Where can I see the current SET50 Index constituents?
Stock Exchange of Thailand publishes the current constituent list. Swoopr does not republish it, because index providers license constituent data and Swoopr holds no such licence.