Ibex 35 today, Friday, August 21: Santander and the banks push the index again towards 19,900 points

The Ibex 35 is the main stock market index of the Spanish Stock Exchange, and its calculation and composition are regulated by very precise technical rules, supervised by the Technical Advisory Committee (CAT) of the index and, ultimately, by BME (Bolsas y Mercados Españoles). Understanding how it is calculated and reviewed allows one to see which companies enter, leave, or gain weight in the indicator used as a reference for Spanish equities.

Daily calculation of the Ibex 35

The Ibex 35 is a free-float market capitalization weighted index. This means that each company weighs according to the market value of the shares actually tradable on the market (those not held by stable or locked-in shareholders).

• Adjusted capitalization: for each company, the number of shares admitted to trading is multiplied by their price, but only the percentage of free float capital is considered. If a company has 60 % free float, only that 60 % of its shares is taken for the calculation.
• Maximum weighting: there is usually a limit to the weight of a single company (for example, 20 %) to prevent the index from depending excessively on a few stocks. If a company exceeds that cap, its weight is "cut" and the excess is redistributed among the rest.
• Index formula: the Ibex 35 is obtained by summing the adjusted capitalizations of the 35 companies and dividing by a divisor. This divisor is modified to neutralize purely technical effects (capital increases, stock splits, extraordinary dividends in kind, etc.) and maintain the continuity of the series.
• Intraday update: during the session, the index is constantly recalculated with the latest trading prices of each stock. Thus, it reflects in real time the aggregated market evolution.

Basic requirements to be part of the Ibex 35

The index is not simply made up of the 35 largest companies, but of those that best meet certain size and liquidity criteria:

• Minimum capitalization: a minimum level of free-float adjusted capitalization is required to be eligible. In practice, almost always the largest companies of the continuous market are considered.
• Liquidity: this is a key criterion. It is measured, among others, by the effective traded volume (in euros) and by the trading frequency (percentage of sessions in which the stock had trades). It is required that the stock has sufficient turnover so that the index is investable and representative.
• Listing age: normally a minimum trading period is required (for example, six months) for the company to be included, except in exceptional cases of large IPOs.

Composition review process

The composition of the Ibex 35 is reviewed periodically and can also be modified extraordinarily:

• Ordinary reviews: generally carried out twice a year (usually in June and December). The Committee analyzes capitalization and liquidity data from recent months for all continuous market stocks.
• Review methodology: stocks are ranked by traded volume and adjusted capitalization. Those already in the index can be replaced by others with higher liquidity and size if they fall below certain positions in that ranking, while new candidates enter if they rise steadily.
• Extraordinary reviews: can be convened if a relevant event occurs: delistings, mergers, takeovers that leave a very reduced free float, etc. In these cases, the Committee can decide the immediate exit of a stock and its replacement without waiting for the next ordinary review.
• Market communication: Committee decisions (entries, exits, and weighting changes due to weight limits or free float adjustments) are announced in advance and applied on a specific date, usually at the close of a session so intermediaries can adjust their portfolios.

Objective of the index rules

Overall, the calculation and review process aims for the Ibex 35 to be:

• Representative of the main Spanish companies and key sectors.
• Investable, so that a manager can replicate it with reasonable costs.
• Stable but flexible: it does not change frequently, but adapts when market reality evolves.

Therefore, composition adjustments tend to be relatively infrequent, but when they occur they tend to reflect structural changes in the Spanish market (new large companies, declines in relevance of others, concentration processes, etc.).

The National Institute of Statistics (INE) is the central body of the official state statistics in Spain and plays a key role in the preparation of economic statistics. Its competencies are based on state statistical regulations (especially the Public Statistical Function Law) and on commitments derived from Spain's membership in the European Statistical System.

Firstly, the INE is the body responsible for the preparation of the main macroeconomic statistics of the country. Among them are:

• National accounts: the INE prepares the Gross Domestic Product (GDP) and the rest of the quarterly and annual national accounts, following the standards of the European System of Accounts (ESA). This includes estimation from the production, demand, and income sides, as well as disaggregation by branches of activity and institutional sectors.
• Price indices: it is responsible for the Consumer Price Index (CPI) and other price indices (such as some industrial or services price indices), which are essential for monitoring inflation, updating contracts, and economic policy.
• Economic conjuncture statistics: it develops surveys and series on industrial production, trade, services, tourism, construction, employment, and other areas that allow analysis of the short-term economic cycle.

Secondly, the INE fulfills a coordination function of the state public statistical system in economic matters. This implies:

• Designing and coordinating the National Statistical Plan, where the statistical operations of the General State Administration are programmed, many of them of an economic nature (production, companies, foreign trade, labor market, etc.).
• Harmonizing concepts, definitions, and classifications used by different ministries and agencies so that economic statistics are comparable and coherent among themselves and with European Union standards.
• Collaborating with the statistical services of the autonomous communities when their data are integrated into state-level statistics, ensuring methodological homogeneity.

Thirdly, the INE has competencies in the collection and processing of primary data necessary for economic statistics:

• It conducts direct surveys to companies and households (for example, business structure surveys, household budget surveys, employment, innovation, ICT in companies, etc.), which provide the empirical basis for many economic statistics.
• It uses and cleans administrative records from other administrations (tax, Social Security, registries, etc.), integrating them into its operations to reduce response burden and improve the quality of economic information.

Fourthly, the INE has a relevant role in the European and international context:

• It is part of the European Statistical System, coordinated by Eurostat, and is obliged to produce and submit a wide set of harmonized economic statistics (national accounts, public deficit and debt, harmonized inflation, business statistics, regional statistics, etc.).
• It participates in technical working groups where common methodologies, dissemination calendars, and quality standards for economic statistics are defined.

Additionally, the INE holds the responsibility to guarantee the quality, impartiality, and confidentiality of economic statistical information:

• It defines and applies statistical quality standards (relevance, accuracy, timeliness, coherence, comparability, and accessibility) and systematically evaluates its economic operations.
• It ensures the confidentiality of individual data (companies and persons), so that information is only used for statistical purposes and can never directly identify respondents.

Finally, the INE has the competence of official dissemination of the State's economic statistics:

• It publishes pre-announced dissemination calendars, made public to reinforce legal certainty and neutrality of relevant economic information.
• It makes available to citizens, companies, analysts, and administrations a wide catalog of databases, time series, and anonymized microdata, allowing in-depth analysis of the Spanish economy.

Overall, the INE not only "produces" figures but structures and leads the State's public economic statistical system, ensuring that the data underpinning the preparation, monitoring, and evaluation of economic policies are rigorous, comparable, and transparent.

The latest general elections in Spain were held on July 23, 2023 (known as 23J) and led to the current XV Legislature of the Congress of Deputies, composed of 350 seats. The Popular Party (PP) was the most voted force in seats and the Spanish Socialist Workers' Party (PSOE) came in second. Completing the core of the main state-wide forces with greater representation are Vox and Sumar, along with several territorial parties that obtained fewer seats.

Basic results of 23J: main state-wide parties

Based on official and polling comparisons referencing 23J, the results picture for the major state-wide parties can be reconstructed:

• Popular Party (PP): obtained 137 seats and around 33.1 % of the vote in the 2023 general elections. Various subsequent analyses use this 23J result as a reference to compare the PP's future seat estimates, explicitly citing those 137 deputies and 33.1 % as a starting figure.
• Spanish Socialist Workers' Party (PSOE): secured 121 seats and about 31.7 % of the votes. Polls reviewing the legislature's evolution start from that data (121 seats and 31.7 %) to measure later losses or gains of the PSOE.
• Vox: achieved 33 seats and approximately 12.4 % of the votes. Numerous polls published in 2025–2026 repeatedly cite those 33 deputies as their current representation "from 23J", then projecting very significant growths on that basis.
• Sumar (coalition then led by Yolanda Díaz): obtained 31 seats and around 12.3 % of the vote when running as a joint candidacy that included Podemos. Subsequent polls compare Sumar's current situation with those 31 deputies obtained in the 2023 general elections.

These four parties concentrate a very large majority of the Chamber and structure state politics: PP and Vox in the right and far-right bloc, and PSOE and Sumar in the national left bloc.

Territorial parties with representation

Alongside the state-wide forces, the 23J elections brought in several regional or territorial parties, completing the Congress map and proving decisive for majority arithmetic. A Government note on the distribution of subsidies to parties with seats in the Congress details which formations obtained representation and, therefore, have received funding proportional to their votes and seats (see information on subsidies).

Among those parties with parliamentary representation are:

• Esquerra Republicana de Catalunya (ERC)
• Junts per Catalunya (Junts)
• Euskal Herria Bildu (EH Bildu)
• Basque Nationalist Party (PNV)
• Galician Nationalist Bloc (BNG)
• Canarian Coalition (CC)
• Navarrese People's Union (UPN)

Polls projecting future scenarios usually take this distribution of territorial forces for granted, and in some cases explicitly reference the 2023 results (for example, indicating that Junts would lose "one seat compared to the 2023 elections" or that the PNV would go from five to four deputies in an estimate). Although those projections look to the future, they serve to confirm that, after 23J, these parties each have a small number of seats but with very high influence capacity because they can tip tight majorities.

Who has the most representation in the current Congress

Focusing on parliamentary representation — that is, how many seats each party has in the Congress resulting from the 2023 elections — the order of forces, by group size, is clearly as follows:

• 1st PP, as the largest group, with 137 deputies.
• 2nd PSOE, second force, with 121 deputies.
• 3rd Vox, with 33 deputies.
• 4th Sumar, with 31 deputies.
• At a considerable distance, the groups of ERC, Junts, EH Bildu, PNV, and BNG; and, with even less representation, CC and UPN.

Since the constitutive session of the XV Legislature (August 17, 2023), there have been numerous individual resignations from seats, replaced by other candidates from the same lists, so the same distribution of seats by party that came out of the polls is maintained, although some faces have changed (information on deputy replacements).

In summary: the latest general elections (23J 2023) gave a very fragmented Congress, in which the PP is the party with the most representation, followed by the PSOE, and where Vox and Sumar complete the block of major state-wide forces, while various nationalist and regionalist parties add the necessary seats to articulate any government majority or to approve the main laws.