--- title: "SET100 Index: Methodology" description: "SET100 Index is maintained by Stock Exchange of Thailand and covers Thai large-cap equity benchmark. How the index selects and weights its constituents." canonical: https://www.getswoopr.com/stocks/indexes/set100/ source: "Swoopr Investment: https://www.getswoopr.com" --- # SET100 Index: What It Measures and How It Is Built ## Direct Answer > The SET100 Index is a rule-based measurement of Thai large-cap 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 SET100 Index covers Thai large-cap 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 100 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 SET100FF 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, excluding property funds, REITs and infrastructure funds. A security needs at least 20 percent free float and a clean standing on bankruptcy, default and audit opinion. The 100 largest by market cap among those passing 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 must not be in a prolonged suspension. 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. Reserve securities are those meeting all qualifications and ranked 101st onward. 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 If too few securities pass the liquidity tests, the number of qualifying months is gradually reduced, though never below 6 months, so the liquidity bar can loosen to fill the index. ## References - [Stock Exchange of Thailand: Stock Exchange of Thailand Ground Rules for SET Index Series](https://media.set.or.th/set/Documents/2025/Feb/Index_Ground_Rule_EN.pdf), as published 2026. Every rule described on this page is taken from this document. ## Current SET100 Index constituents Stock Exchange of Thailand publishes and licenses the SET100 Index constituent list. Swoopr does not republish it here. The provider's own page is the authoritative source for current membership and weights. [Stock Exchange of Thailand: official SET100 Index page](https://www.set.or.th/en/market/index/setindex) ## Related reading - [All stock market indexes](https://www.getswoopr.com/stocks/indexes/): how indexes are built, weighted and revised. - [Emerging Markets indexes](https://www.getswoopr.com/stocks/indexes/emerging-markets/): others covering the same region. - [Index concentration](https://www.getswoopr.com/technical-analysis/market-concentration/index-concentration/): measuring how much of an index sits in its largest holdings. - [Index rebalancing and inclusion effects](https://www.getswoopr.com/stocks/corporate-actions-catalysts/index-rebalancing-and-inclusion-effects/): what happens to a stock when index membership changes. ## Frequently Asked Questions ### Who maintains the SET100 Index? Stock Exchange of Thailand maintains the SET100 Index and publishes the methodology document that defines its eligibility and weighting rules. ### What does the SET100 Index measure? It measures Thai large-cap 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 SET100 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. ## About the author The [Swoopr Editorial Team](https://www.getswoopr.com/authors/swoopr-editorial-team/) writes Swoopr Investment's educational library, covering market structure, analysis methods and the mechanics behind the numbers investors read every day. Our [editorial policy](https://www.getswoopr.com/legal/editorial-policy/) and [corrections policy](https://www.getswoopr.com/legal/corrections-policy/) set out how this content is produced, reviewed and fixed when it is wrong.