Borsa Istanbul Trading Rules: Market Segments, Price Limits, Market Makers, Halts and Official Auctions under the Equity Market Directive

How a share trades on Borsa Istanbul is not fixed by the market alone. The exchange’s Equity Market Directive places each listed share in a market segment, the Star Market, the Main Market, the Sub-Market, the Watchlist Market or the Pre-Market Trading Platform, using criteria such as market value, free float, liquidity, volatility, equity and, for the Star Market, holdings by Turkish investment and pension funds (Equity Market Directive Art. 37). The segment determines whether short selling and margin trading are allowed, whether trades settle gross, how far the price may move in a session and when circuit breakers trigger (Art. 39). In disputes, the exchange’s records prevail (Art. 24(2)). The General Manager may halt trading in a share for up to a month and, when doing so, may cancel orders already entered and trades already executed (Art. 30). Market makers may, after notifying the exchange, use accounts that are not their own, and liquidity providers may obtain shares from a company’s shareholders under an agreement approved by its board (Arts. 28 and 29). Shares attached by courts and enforcement offices, including shares in sub-accounts of brokers whose activities have been stopped, are sold through official auctions (Art. 32). This guide explains these rules and why they matter to foreign institutional investors. It reflects the Equity Market Directive as revised on 21 September 2026 and the legislation in force as at 25 October 2026.

Why exchange trading rules matter in the 2026 cases

Allegations of market manipulation are, at bottom, allegations about how prices were formed on the exchange. The rules of Borsa Istanbul’s Equity Market determine much of that process: which shares can be bought on credit or sold short, whether trades are netted or settled one by one, how far prices can move in a day, when trading stops automatically, who may act as market maker and with which accounts, and how the exchange can intervene. They also determine which records exist, and the Directive says that, in a dispute, the exchange’s records prevail.

For a foreign institutional investor, these rules matter in three ways. They explain how the price of a share it holds could move as it did and what constraints applied. They identify the measures the exchange took on a share and the documents those measures generated. And they define the investor’s own position when a share is halted, moved to another segment, or when attached shares are sold through an official auction. The earlier guide to trading halts, the Watchlist Market and delisting covers halts under the Exchange Activities Regulation, gross settlement and deposit measures, the Watchlist Market and delisting. This guide covers the rest of the Equity Market Directive.

The guide does not suggest that any person or company connected with the 2026 cases breached exchange rules or that any exchange decision was wrong.

The legal framework

Borsa Istanbul is a joint stock company subject to private law that performs its statutory functions independently (Capital Markets Law Art. 65(10)); the rules on listing, trading, order matching, settlement, membership, discipline, disputes and surveillance are set out in a regulation prepared by the exchange and approved by SPK (Art. 67(1)), supplemented by directives adopted by its board. The Equity Market Directive is based on the Exchange Activities Regulation published in the Official Gazette of 19 October 2014 (No. 29150) (Equity Market Directive Art. 3). It governs orders and trades, reports, recorded prices, trading methods, market making and liquidity provision, halts, special transactions, settlement methods and the criteria for distributing shares among market segments (Art. 2).

The Directive is an exchange instrument, not a statute, and its thresholds and parameters can be changed by the exchange’s board, in some cases with SPK’s approval. The figures in this guide are those of Revision 18.

Market segments and how shares are classified

Shares that have been listed and started trading are assessed at least twice a year, at times set by the General Manager, against the criteria in the Directive, and their segment is changed according to the results; the criteria can be changed by the exchange’s board with SPK’s approval (Equity Market Directive Art. 37(1)). The assessment uses one-year averages of the data for each criterion (Art. 38(1)).

Shares that do not meet the Main Market criteria are placed in the Sub-Market. Each share must meet all criteria of its segment, subject to three exceptions for shares with a free float above 5 per cent: very large and liquid shares meeting the Star Market volatility and equity criteria go to the Star Market, and two categories of Sub-Market shares with high free-float value and either high dividend yield or good liquidity go to the Main Market (Art. 37(3)). A share that would jump from the Star Market to the Sub-Market, or the other way, goes to the Main Market for one period (Art. 37(4)). Shares with a free float below 5 per cent may be moved to the Pre-Market Trading Platform (Art. 37(5)).

Three definitions deserve attention. “Domestic fund holdings” means the average market value, over the last year, of the part of the share held in the portfolios of investment funds and pension investment funds supervised by SPK, according to Central Registry Agency (MKK) data (Art. 37(2)(d)). The volatility criterion asks whether the share is in the highest volatility band, set at no more than the top 10 per cent of assessed shares (Art. 37(2)(g)). The liquidity criterion measures the average intraday cost, in basis points, of buying and selling TL 1 million at any time (Art. 37(2)(e)).

Trading parameters by segment

The segment determines the trading rules that apply (Equity Market Directive Art. 39(1)). The General Manager may change them for a particular share, taking into account its liquidity and other market conditions (Art. 39(3)).

The “equity value” ratio shows up to what proportion a share may be counted as equity in the account used for margin purchases, short sales and securities lending; the “open settlement position” ratio shows the minimum equity that must be held against an open settlement position in the share until settlement (Art. 39(1)(a)–(b)). The Directive’s table shows that cancelling, worsening or reducing orders in the last five minutes of the opening session is not available in any segment (Art. 39(1)). SPK’s exceptions allowing purchase orders without collateral for clients with sufficient assets apply only to Star Market shares, and for collective investment schemes and pension funds also to Main Market shares (Art. 39(4)–(5)).

In practice, moving a share from the Main Market to the Sub-Market removes margin trading and short selling, imposes gross settlement, narrows the daily price margin and makes the circuit breaker more sensitive. These are the same kinds of measure that SPK may impose under Article 101(1) of the Capital Markets Law where manipulation or market-disrupting acts are suspected, as explained in the guide to market-disrupting acts.

Orders, priority and sessions

Orders are sent to the trading system by exchange members through their assigned interfaces and terminals (Equity Market Directive Art. 5(1)). Orders not yet executed may be amended, corrected or cancelled under rules set by the exchange’s board (Art. 8(1)). Matching follows price priority and then time priority: lower-priced sell orders and higher-priced buy orders execute first, and at equal prices the earlier order executes first (Art. 9(1)); shortening an order’s validity keeps its time priority, while extending it loses priority (Art. 7). Limits on capacity, quantity or amount can be imposed on particular users as pre-trade risk controls, and the General Manager can change them on his own initiative in unusual market conditions (Art. 10(1)).

Two trading methods are used. In the single-price method, orders are collected over set periods and matched at the single price that maximises traded quantity; during order collection no trades take place and orders can be cancelled or changed (Arts. 25(2) and 26(1)(a)). In the multi-price, or continuous, method, orders are matched continuously at different price levels as they arrive (Arts. 25(3) and 26(1)(b)). The opening and closing prices are set in single-price opening and closing sessions (Arts. 15 and 16). Opening and closing prices matter for valuations, index calculations and fund pricing, which is why transactions aimed at affecting them are listed as market-disrupting acts (Communiqué VI-104.1 Art. 5(1)(d)).

Price limits and recorded prices

The base price is the price from which the upper and lower limits for a session are calculated; depending on the board’s decision, it is the previous session’s closing price or the volume-weighted average price of the previous session rounded to the nearest tick (Equity Market Directive Art. 18(1)). Prices are adjusted for corporate actions such as dividends, capital increases, mergers and demergers (Art. 18(2)). The percentage applied to the base price to set the price change limits is determined by the exchange’s board and may differ by session, segment, instrument or order type (Art. 20(1)–(3)). The head of the Equity Market department may, where the market requires, double the limit for a share for that session, and the General Manager may remove or change the limits (Art. 20(4)). Price ticks by price band are set by the General Manager and announced on KAP at least a day in advance (Art. 19).

A trade is recorded as an exchange price if it is for at least one lot, and the board may change the minimum quantity by announcement on KAP at least a day in advance (Art. 21(1)). Recorded prices and quantities are published in the exchange’s daily bulletin after the session (Art. 22).

Market data and the exchange’s records

Trade data (price, quantity, amount) and order book depth are published in real time or with a delay on members’ screens and through data vendors, as determined by the exchange’s board (Equity Market Directive Art. 23). After each session, trade results are made available electronically to members, who use them to keep their own legal records; in any dispute, the exchange’s records prevail (Art. 24(1)–(2)).

This rule shapes evidence in any case about trading. The exchange holds the authoritative record of orders and trades. A broker’s records should match it, and the broker’s own records of electronic orders, including cancelled and modified orders, must be kept with time stamps (Communiqué III-37.1 Art. 35(2)(d)). In a civil claim or a criminal case concerning trading in a share, the exchange’s order and trade data, obtained through SPK, the prosecutor or the court, are the starting point. How to obtain them is discussed in the guide to obtaining and preserving evidence.

Market makers and liquidity providers

A market maker is an investment firm authorised by the General Manager, under criteria set by the board, to ensure the fair, orderly and efficient functioning of the market in an instrument and to contribute to liquidity; its performance is assessed periodically (Equity Market Directive Art. 4(1)(ö)). It contributes to price formation by entering quotes or orders in its own name and for its own account (Art. 28(1)). It may also use accounts that are not its own for these transactions, provided it notifies the exchange at least one business day in advance; using such accounts does not remove its market-making obligations (Art. 28(2)). Its quotes are assessed on spread, size and time in the book, and after two consecutive periods below the thresholds it is warned and after a third its role may be ended (Art. 28(5)). The General Manager may end market making on his own initiative where necessary for the sound functioning of the market (Art. 28(8)).

A liquidity provider supports liquidity in an instrument by sending orders or quotes, in its own name for its own account or for the account of others (Art. 29(1)). In shares, it may obtain shares from the company’s shareholders, and it may start only after the company’s board has adopted a decision permitting the transactions and the company and the liquidity provider have entered into an agreement (Art. 29(3)–(4)). Market making and liquidity provision may not be carried on in the same instrument (Arts. 28(7) and 29(6)).

These rules connect with other parts of the law. Price stabilisation and market making carried out in accordance with SPK’s rules are not manipulation or insider dealing (Capital Markets Law Art. 108(1)(c)). Sales by large shareholders that would otherwise require a share sale information form are exempt when made within liquidity provision or market making (Share Communiqué VII-128.1 Art. 27(8)). For an investor reviewing heavy selling or buying in a share, whether a market maker or liquidity provider was appointed, which accounts it used, and whether shareholders supplied shares to it are therefore relevant facts. The share sale information form regime is explained in the guide to market-disrupting acts.

Halts, cancellations and long suspensions

The General Manager may halt trading in an instrument for up to one month, and longer only by decision of the exchange’s board, where (Equity Market Directive Art. 30(1)):

1. (a) there is uncertainty about the instrument or its issuer, or information important enough to affect investors’ decisions, and the General Manager considers that investors should be informed;
2. (b) orders at unusual prices or quantities are entered in a way that prevents a sound market from forming;
3. (c) there is important information about the market maker or liquidity provider that may affect its role and should be disclosed;
4. (ç) systemic, communication, technical or similar problems prevent the session from running properly.

A halt is announced on KAP with its reasons. When trading is resumed, the General Manager may reset the base price, and he may cancel, in whole or in part, orders already entered and trades already executed (Art. 30(3)). Where a halt extends beyond the session, the time of resumption and any base price are announced on KAP (Art. 30(4)). The board may give the issuer up to two years from its decision to remove the uncertainty, and at the end of that period decides, with reasons announced on KAP, whether to reopen trading or ban it (Art. 30(5)).

Circuit breakers operate automatically within the continuous method when price changes reach the thresholds set for each segment (Art. 27), and the General Manager may also halt the whole market or segments by reference to an index (Art. 27(2)). Unusual situations in the trading system may lead to sessions not starting or being stopped (Art. 42).

Block trades, special trade notifications and official auctions

Large trades above an amount set by the General Manager in a company’s shares, whether or not they are listed, are carried out as block trades; these include sales of new shares from capital increases and sales of existing shareholders’ shares to pre-agreed buyers or qualified investors, and details are announced on KAP before and after the trade (Equity Market Directive Art. 31(1)–(3)). Members may also report matched buy and sell orders within set price, quantity and amount limits for conversion into trades without entering the order book; their quantities are included in market totals and their details are published separately in the bulletin (Art. 36).

Courts, enforcement offices and other official bodies that need shares sold on the exchange must apply in writing, with documents confirming that the shares have been attached at MKK or the settlement institution (Art. 32(1)–(2)). The sale takes place in the share’s normal order book or in a separate official auction order book announced on KAP the day before (Art. 32(3)–(4)), and is carried out primarily by the investment firms at which the debtors’ accounts are held (Art. 32(5)). Where shares in the sub-accounts of investment firms whose activities have been stopped are attached and an official body requests their sale, the exchange carries out the sale after confirmations from MKK and/or the settlement institution and transfers the proceeds, net of commissions and legal deductions, to the requesting body (Art. 32(6)).

New share rights are traded in separate order books during the rights period until five trading days before its end (Art. 34). Shares offered in public offerings through the exchange are sold in the primary market under rules set within SPK’s framework (Art. 33), and trades executed in such offerings are not cancelled at the request of the issuer or intermediary unless there is a material error (Art. 33(6)). Public offerings are explained in the guide to public offerings.

Settlement, defaults and member collateral

Settlement obligations from equity trades follow the rules of the settlement institution (Equity Market Directive Art. 43), and default transactions are executed on the settlement institution’s notification to close settlement gaps on the same day (Art. 35). Members must deposit equity market collateral calculated by the board, and members whose collateral is incomplete may not trade until it is completed (Art. 45(1)–(2)). If a member defaults in one market and its collateral there is insufficient, its collateral in other markets of the exchange may be used to cover the shortfall so that the non-defaulting member can collect (Art. 45(3)–(4)). The protection of client assets when a broker fails is explained in the guides to investment services rules and insolvency and client assets.

Challenging exchange decisions

Borsa Istanbul is subject to private law, and actions against it are brought in the civil courts (Capital Markets Law Art. 65(10)–(11)). Decisions on segment changes, halts, cancellations and trading parameters are therefore challenged in the civil courts rather than by administrative annulment actions; the exchange’s dispute procedures and SPK’s supervisory role are explained in the guide to trading halts, the Watchlist Market and delisting. Measures imposed by SPK itself under Article 101 are administrative decisions and are challenged in the administrative courts, as explained in the guide to suing the Capital Markets Board.

The exchange’s tools and SPK’s tools overlap but come from different sources and are challenged in different courts. The table below sets them side by side.

What these rules mean for investors

Four practical consequences follow. First, a share’s segment at a given time tells an investor which trading constraints applied: whether short selling and margin were available, how wide the daily band was and whether trades settled gross. This affects how losses arose and what alternative trading was possible. Second, the exchange’s records prevail in disputes (Art. 24(2)), so any analysis of trading should be built on exchange data. Third, the roles of market makers and liquidity providers, including market makers’ use of other accounts and liquidity providers’ supply of shares from shareholders, should be checked whenever trading volumes are examined. Fourth, halts can lead to cancelled trades and long suspensions, and official auctions can sell attached shares, including those held at suspended brokers, so an investor’s position may change without its own action.

Points for foreign institutional investors

1. 1. Track segment changes. Follow the exchange’s periodic assessments and KAP announcements for the shares held; a move to the Sub-Market or the Watchlist Market changes settlement, price limits and the availability of short selling (Equity Market Directive Arts. 37–39).
2. 2. Watch the fund criterion. For Star Market shares, domestic fund holdings are part of the classification (Art. 37(2)(d)); concentrated fund ownership in a holding is worth noting.
3. 3. Check market makers and liquidity providers. KAP disclosures and company board decisions show whether a liquidity provider was engaged and on what terms (Art. 29(4)).
4. 4. Reconcile with exchange data. Where a broker’s records and the exchange’s records differ, the exchange’s records prevail (Art. 24(2)).
5. 5. Prepare for halts. Trades around a halt may be cancelled (Art. 30(3)); keep records of orders sent and confirmations received.
6. 6. Follow official auctions. Where a broker’s activities have been stopped and shares in its sub-accounts are attached, official auction sales may follow (Art. 32(6)); confirm the position of your own holdings with MKK and your custodian.

Time limits and periods

Frequently asked questions

How are Borsa Istanbul shares assigned to market segments?

The exchange assesses listed shares at least twice a year against criteria on market value, free float, domestic fund holdings, liquidity, volatility and equity, using one-year averages (Equity Market Directive Arts. 37 and 38).

Can short selling be used in all Borsa Istanbul shares?

No. Short selling and margin trading are available in the Star and Main Markets but not in the Sub-Market, the Watchlist Market or the Pre-Market Trading Platform (Art. 39(1)).

Which shares settle gross?

Shares in the Sub-Market, the Watchlist Market and the Pre-Market Trading Platform (Art. 39(1)); the exchange and SPK may also impose gross settlement on particular shares.

What is the daily price limit on Borsa Istanbul?

Under Revision 18 the price margin is 20% in the Star Market, 15% in the Main Market and 10% in the other segments (Art. 39(1)); limits can be changed for a share or session (Art. 20(4)).

Whose records prevail in a dispute about trades?

The exchange’s records (Art. 24(2)).

Can Borsa Istanbul cancel executed trades?

Yes. When trading in a halted instrument resumes, the General Manager may cancel orders and executed trades in whole or in part (Art. 30(3)).

How long can a share be halted?

Up to one month on the General Manager’s decision and longer by board decision; the board may give the issuer up to two years to remove the uncertainty before deciding to reopen trading or ban it (Art. 30).

Can a market maker trade through other people’s accounts?

Yes, if it notifies the exchange at least one business day in advance; its market-making obligations continue (Art. 28(2)).

Where do liquidity providers get shares?

They may obtain shares from the company’s shareholders, after the company’s board permits the transactions and an agreement is signed (Art. 29(3)–(4)).

How are attached shares sold?

Through official auctions on the exchange at the request of courts or enforcement offices, including shares in sub-accounts of investment firms whose activities have been stopped (Art. 32).

Related guides

• Turkey’s 2026 Fund and Market Manipulation Crisis: Legal Guide for Foreign Institutional Investors — the entry point to this series
• Turkish Currency Law and Repatriation of Investment Proceeds
• Turkish Book-Entry Securities and the Central Registry (MKK)
• Trading Halts, Watchlist Market and Delisting on Borsa Istanbul
• Market-Disrupting Acts in Turkey: Article 104 and Communiqué VI-104.1
• Market Manipulation under Turkish Law: Article 107
• Investment Services Rules in Turkey: Communiqués III-37.1 and III-39.1
• Turkish Investment Fund Rules: Communiqués III-52.1, III-55.1 and III-56.1
• Public Offerings in Turkey
• Obtaining and Preserving Evidence in Turkey for Securities Claims
• Suing the Capital Markets Board in Turkey