What is Ibex 35?

The IBEX 35 is the benchmark stock market index of the Spanish stock exchange, and it measures the joint behaviour of the 35 most traded companies (those that arouse the greatest and most frequent buyer and seller interest among shareholders), from among those listed on the Electronic Stock Market Interconnection System (SIBE) in the four Spanish stock exchanges (Madrid, Barcelona, Bilbao and Valencia).

Which companies make up the Ibex 35?

The Ibex 35 is made up of the companies in the Spanish stock market which, after an analysis by the technical advisory committee, best meet the parameters of:

  • Capitalisation
  • Liquidity
  • Volume traded

It is therefore somewhat of a myth to assume that it is necessarily the largest companies in the market that make up the Ibex 35, as it is more like an average of these indicators. However, it is a market capitalisation-weighted index (number of shares in circulation by price per share), i.e. not all the securities included in it have the same weighting.

Large-cap companies have more and, therefore, their ups and downs will have a greater influence on the movement of this index, so you have to watch them very carefully.

The Ibex 35 shows the state of the stock market and is a good indicator of the state of the Spanish economy. In fact, analysing its evolution since its creation on 14 January 1992, you can get an idea of what has happened to the Spanish stock market over the last twenty years.

How are the stocks that form part of the Ibex 35 index chosen?

The Ibex 35 is made up of the 35 most important companies in Spain. The selection of these is decided by a group of experts known as the Technical Advisory Committee (CAT), which meets twice a year (usually in June and December, although extraordinary meetings can be held) to evaluate the importance of companies on the stock market. To do so, they take into account certain factors such as:

  • Unit price per share.
  • Change in percentage and in euros with respect to the previous session.
  • Volume of shares traded in a session, specified in euros.
  • Capitalisation: is the market value of the company, the number of shares in circulation multiplied by the price of each one.
  • PER: is an indicator which, calculated in reverse, indicates the return on investment over the year if that value were to remain constant.

Dividend yield: is the result of dividing the expected dividend by the price of each share.

What does a share have to have in order to be part of the Ibex 35?

For a share to be an Ibex 35 candidate, it must pass some minimum filters:

  • Average capitalisation. The average capitalisation of the future member must be greater than 0.30% of the average capitalisation of the Ibex 35 during the control period (the six months between meetings).
    This means excluding small-cap stocks.
  • Trading. The second filter establishes that the stock must have been traded in at least one third of the sessions during the control period.

Ranking. If the latter were not the case, this stock could still be selected if it were among the 20 with the highest capitalisation.

How is the Ibex 35 calculated?

The mathematical formula used to calculate the value of the Ibex 35 is based on the capitalisation of each of its component stocks, as well as an adjustment coefficient, which is applied so as to prevent possible financial transactions (such as capital increases, reductions...) affecting its value.
The formula is as follows:


To calculate the value of the Ibex 35 on a given day, we start with that of the previous session. This value is multiplied by a percentage obtained by dividing the current sum of the capitalisations of the 35 companies in the Ibex, by the sum of the capitalisations of the index values of the previous day.

If there have been any strange operations that could distort the result, then a corrective weighting value (J) is applied to the latter capitalisations.

The capitalisation of a stock or company in the Ibex 35 is obtained by multiplying the number of shares of each company by the market value on the given day.

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