What is the BIST 100? Turkey's main stock index explained

The BIST 100 is the benchmark index of Borsa Istanbul, Turkey's stock exchange. It follows 100 companies selected from the exchange's main market for their size and trading activity, and its code is XU100. When Turkish news says that the borsa rose or fell today, it usually means this index.

The index covers many sectors, including banking, airlines, energy, steel, retail and holding companies. That makes it a quick read on how investors feel about the Turkish economy as a whole.

Like most major indices, the BIST 100 is weighted by market value, and only the shares freely available to trade count. Each company's weight follows its free-float market capitalisation:

Weight of a stock = free-float market cap ÷ total free-float market cap of the 100
Index return      = sum of (weight × stock return)

The member list is reviewed every three months, so companies can enter or leave as their size and liquidity change. The level itself is a number with no currency, but it reflects prices in Turkish lira.

A rising BIST 100 in lira can still be a weak result in real terms. With high inflation and a weaker lira, nominal gains may be small once measured in prices or in dollars. Comparing the index with inflation and with USD/TRY gives a fairer picture.

Because a few large names carry big weights, a move in a handful of banks or holdings can dominate a day. Look at breadth, meaning how many members rose, as well as the headline number.

You cannot buy an index directly. Investors usually hold BIST 100 index funds or exchange-traded funds, or buy the member shares themselves. Index futures also exist for hedging and trading, but they are leveraged and carry high risk.

Past performance does not predict future returns, and an index can fall sharply in a downturn.