Direct Answer
The BIST 100 is a rule-based measurement of Turkish large-cap equity benchmark, maintained by Borsa Istanbul. 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 BIST 100 covers Turkish large-cap equity benchmark, within the Turkey market. Borsa Istanbul 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
Weighted by free float market value: number of shares times price times free float ratio times a weighting factor. The headline index is uncapped, while capped versions with a 10% or 25% capping ratio are calculated separately and trimmed daily if a weight passes the 15% or 30% threshold. Versions exist in lira, dollars and euros, price and return.
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
100 stocks of companies traded on the Stars Market. The selection pool holds stocks that have traded at least 60 days, and uses only Stars Market stocks if 113 or more remain. If fewer than 113 remain, stocks from an exchange market grouping list are added, and if fewer than 110, stocks from the previous review are added. Investment trusts and Watchlist Market stocks are excluded.
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 stock needs at least 60 days of trading to enter the selection pool, except a large IPO: if its market value at the end of the offering exceeds one twentieth of the free float market value of BIST 30, it joins from the fifth trading day in place of the smallest member.
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 quarterly on the last day of November, February, May and August using 12 months of traded value and average prices. New index periods run January to March, April to June, July to September and October to December and are announced at least 10 days before each starts.
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
Stocks are ranked on two lists, average free float market value and daily traded value, and the final rank rewards placing high on both. A stock enters at rank 90 or better and leaves only below rank 110, with three substitutes named for mid period vacancies.
References
- Borsa Istanbul: Borsa Istanbul, BIST Market Cap Weighted Stock Indices Methodology, September 2026 edition, as published 2026. Every rule described on this page is taken from this document.
Current BIST 100 constituents
Borsa Istanbul publishes and licenses the BIST 100 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 BIST 100?
Borsa Istanbul maintains the BIST 100 and publishes the methodology document that defines its eligibility and weighting rules.
What does the BIST 100 measure?
It measures Turkish 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 BIST 100 constituents?
Borsa Istanbul publishes the current constituent list. Swoopr does not republish it, because index providers license constituent data and Swoopr holds no such licence.