--- title: "BUX: Methodology" description: "BUX is maintained by Budapest Stock Exchange and covers Hungarian blue-chip equity benchmark. How it selects and weights its constituents, and what it measures." canonical: https://www.getswoopr.com/stocks/indexes/bux/ source: "Swoopr Investment: https://www.getswoopr.com" --- # BUX: What It Measures and How It Is Built ## Direct Answer > The BUX is a rule-based measurement of Hungarian blue-chip equity benchmark, maintained by Budapest Stock Exchange. 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 BUX covers Hungarian blue-chip equity benchmark, within the Hungary market. Budapest Stock Exchange defines which securities are eligible, how they are selected from that pool, and how much each one contributes to the published number. The index name does not state a fixed company count, so the number of constituents follows the eligibility rules rather than a target. ## How constituents are weighted Free float market capitalization weighted return index that assumes dividends are reinvested in the same share. Weights go through a degression: below 10% unchanged, between 10% and 20% only half of the excess counts, above 20% only a quarter. A liquidity cap based on five days of average turnover against a theoretical 10 billion forint portfolio may reduce weights further. 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 A basket of 12 to 25 share series, one per company. A series must rank in the top 20 by turnover over the last half year and in the top 20 by free float market capitalization on the review date, and an existing member that misses the top 20 stays if it ranks in the top 25 on both lists, unless it also missed both criteria in the previous half year. Free float must be at least 10%. A foreign issuer needs a significant link to the Hungarian economy and a turnover on this exchange of at least 5% of its turnover on all EU regulated markets. 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 newly listed share series must have 15 trading days behind it before entering the basket, and series listed within three weeks before a review are not evaluated. A series that left the index at the previous review cannot return at the current one. 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 Baskets are reviewed twice a year: eligibility is assessed on 1 March and 1 September using the previous half year, and the new baskets start on the first trading day after the end of March or September. The chief executive decides at least two weeks before the change on the Index Committee proposal. 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 largest companies are underweighted by design: above 10% a share counts only half of its excess and above 20% only a quarter, so a stock with a 30% market weight ends well below it. A separate liquidity ceiling can cut weights again. ## References - [Budapest Stock Exchange: Budapest Stock Exchange, Handbook on the Hungarian Indices of the Exchange (BUX, BUMIX), 3 August 2026, Hungarian text](https://bet.hu/pfile/file?path=/site/Magyar/Dokumentumok/Befektetok/BET_szabalyok/Magyar_Indexek_Kezikonyv_20260803.pdf), as published 2026. Every rule described on this page is taken from this document. ## Current BUX constituents Budapest Stock Exchange publishes and licenses the BUX constituent list. Swoopr does not republish it here. The provider's own page is the authoritative source for current membership and weights. [Budapest Stock Exchange: official BUX page](https://bet.hu/site/Angol/Contents/Products-and-Services/Indices/indices) ## Related reading - [All stock market indexes](https://www.getswoopr.com/stocks/indexes/): how indexes are built, weighted and revised. - [Europe indexes](https://www.getswoopr.com/stocks/indexes/europe/): 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 BUX? Budapest Stock Exchange maintains the BUX and publishes the methodology document that defines its eligibility and weighting rules. ### What does the BUX measure? It measures Hungarian 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 BUX constituents? Budapest Stock Exchange 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.