The IBEX 35 is the main stock market index of the Madrid Stock Exchange in Spain. It was founded in 1992 and is made up of the 35 most important companies and enterprises listed on the Spanish continuous market.

This index reflects the performance of the Spanish market and is weighted by market capitalization, which means that companies with a higher market capitalization have a higher weight in the index.

Practically all IBEX 35 companies pay dividends, some of the best known being Banco Santander, Inditex, Repsol, BBVA and others.

How is the value of the Ibex35 calculated?

To determine the daily value of the Ibex 35 stock market index, the following mathematical formula is used based on the capitalization of the companies that comprise it:

Ibex 35(t) = Ibex 35(t - 1) × Σ Capi(t) / [ Σ Capi(t - 1) ± J ]

In addition, an adjustment coefficient J is used to prevent financial operations such as capital increases or reductions from drastically affecting the share price.

The value of the Ibex on day t is obtained by multiplying the value of the Ibex on the previous day (day t-1) by a percentage calculated from the sum of the capitalizations of the 35 companies on day t, divided by the sum of the capitalizations on day t-1.

In case you are not familiar with it, the daily capitalization of a specific company is obtained by multiplying the number of shares by the listed value of that company on that day.

If today the Ibex closed at 10,000 points, the total capitalization of the 35 companies today would be approximately 400 billion. If tomorrow the capitalization, at the close, amounted to 405,000 million, the final closing of the Ibex, tomorrow would be:

Ibex 35 (specific day) = 10,000 x 405/400 = 10,125 basis points.