--- title: "S&P/ASX 20: Methodology" description: "S&P/ASX 20 is maintained by S&P Dow Jones Indices/ASX and covers top 20 companies listed on the Australian Securities Exchange by float-adjusted market cap." canonical: https://www.getswoopr.com/stocks/indexes/sp-asx-20/ source: "Swoopr Investment: https://www.getswoopr.com" --- # S&P/ASX 20: What It Measures and How It Is Built ## Direct Answer > The S&P/ASX 20 is a rule-based measurement of top 20 companies listed on the Australian Securities Exchange by float-adjusted market cap, maintained by S&P Dow Jones Indices/ASX. 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 S&P/ASX 20 covers top 20 companies listed on the Australian Securities Exchange by float-adjusted market cap, within the Australia market. S&P Dow Jones Indices/ASX 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 20 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 Constituents are weighted by float-adjusted market capitalization (FMC) using the standard S&P Dow Jones divisor method. Share counts are reviewed quarterly and rounded to the nearest thousand. 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 Measures 20 actively traded and highly liquid securities that are among the largest ASX stocks by FMC. To be eligible, a stock must be an ASX-listed ordinary or equity preferred share classified by GICS, with an Investable Weight Factor of at least 0.3 and a minimum Relative Liquidity of 50% against the All Ordinaries market liquidity. Listed investment companies and trusts and acquisition targets are not eligible. 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 Market capitalization is measured on a six-month daily average. An IPO or direct listing is added only when a vacancy appears or at a rebalance, and only after proven liquidity for at least eight weeks. An exception may be made for an extraordinary large offering, which the methodology defines as one that could be considered for the S&P/ASX 20 on its relative FMC rank. 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 Rebalanced quarterly, effective after the close on the third Friday of March, June, September and December. Data are taken on the second to last Friday of the prior month, and announcements come on the first Friday of the rebalancing month, giving two weeks of notice. A non-member is considered at rank 14 or higher, and a member is removed at rank 26 or lower. 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 eight week liquidity rule for IPOs has an exception: an extraordinary large offering, defined as one that could rank for the S&P/ASX 20 on relative FMC, can be included early where its sizeable trading volumes justify it. ## References - [S&P Dow Jones Indices/ASX: S&P Dow Jones Indices, S&P/ASX Australian Indices Methodology](https://www.spglobal.com/spdji/en/documents/methodologies/methodology-sp-asx-australian-indices.pdf), as published 2025. Every rule described on this page is taken from this document. ## Current S&P/ASX 20 constituents S&P Dow Jones Indices/ASX publishes and licenses the S&P/ASX 20 constituent list. Swoopr does not republish it here. The provider's own page is the authoritative source for current membership and weights. [S&P Dow Jones Indices/ASX: official S&P/ASX 20 page](https://www.asx.com.au/markets/trade-our-cash-market/overview/indices) ## Related reading - [All stock market indexes](https://www.getswoopr.com/stocks/indexes/): how indexes are built, weighted and revised. - [Asia-Pacific indexes](https://www.getswoopr.com/stocks/indexes/asia-pacific/): 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 S&P/ASX 20? S&P Dow Jones Indices/ASX maintains the S&P/ASX 20 and publishes the methodology document that defines its eligibility and weighting rules. ### What does the S&P/ASX 20 measure? It measures top 20 companies listed on the Australian Securities Exchange by float-adjusted market cap. 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 S&P/ASX 20 constituents? S&P Dow Jones Indices/ASX 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.