Direct Answer
The BUMIX is a rule-based measurement of Hungarian mid-cap 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 BUMIX covers Hungarian mid-cap 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 capitalisation weighted. Above HUF 75 billion of free float capitalisation a share's counted value is scaled down, reaching zero at HUF 125 billion. A degression then trims weights: only half of the excess between 10% and 20% counts and a quarter above 20%.
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
Hungarian regulated market shares must rank in the top 25 on half year turnover and in the top 25 on free float capitalisation on the review day. One share series per company, free float of at least 10%, and a basket of 12 to 25 series. Foreign domiciled issuers need a Hungarian economic link and enough share of EU regulated trading.
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 needs at least 15 trading days after its first trading day before joining the basket, and one listed within 3 weeks before a review is left out of that evaluation.
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
Reviews run twice a year, with evaluation on 1 March and 1 September using the prior half year. New baskets start on the first trading day after the last day of September or March. A member that fails once can stay if it is within the top 30 in both rankings, and leaves if it falls outside the top 30 or fails twice running.
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 BUMIX has a size ceiling: a share whose free float capitalisation exceeds HUF 125 billion cannot enter, and a series removed at a review cannot re-enter at the next one.
References
- Budapest Stock Exchange: Budapest Stock Exchange Handbook of the Hungarian Indices BUX and BUMIX, Magyar Indexek Kezikonyve (August 2026), as published 2026. Every rule described on this page is taken from this document.
Current BUMIX constituents
Budapest Stock Exchange publishes and licenses the BUMIX 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.
- Europe 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 BUMIX?
Budapest Stock Exchange maintains the BUMIX and publishes the methodology document that defines its eligibility and weighting rules.
What does the BUMIX measure?
It measures Hungarian mid-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 BUMIX 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.